image.h: isolate android_image_* functions from tooling

On Feb. 16, 2020, Tom reported [1] build failure of U-Boot in-tree
tooling after applying https://patchwork.ozlabs.org/cover/1229663/
("[v6,0/7] rsa: extend rsa_verify() for UEFI secure boot").

Later on, Heinrich stressed the urgency of the issue in
https://patchwork.ozlabs.org/patch/1250858/#2379069:

 >>>>>>>>>
 We should finalize the topic as it stops EFI patches from being merged
 >>>>>>>>>

On the surface, the problem is caused by U-Boot commits [2-3], which
employed 'u32' in 'include/image.h', while historically U-Boot tooling
stayed agnostic on the {u,s}{8,16,32} types.

Thanks to Tom, Yamada-san and Heinrich, the following solutions have
been put head-to-head ('+' pros, '-' cons):

 A. Use an equivalent fixed-size type, i.e. s/u32/uint32_t/ in both
    android function prototypes (image.h) and definitions (c file):
    + quick and low-line-count
    - creates a 'soup' of fixed-sized types in the Android C file
    - will confuse contributors
    - is going against Linux kernel best practices [4]

 B. Guard Android functions by '!defined(USE_HOSTCC)' in image.h:
    + quick and low-line-count
    + reflects the reality (no android function is used by tooling)
    + zero impact on other subsystems
    - ifdeffery may look annoying (pre-existing problem of image.h)

 C. Make {u8,u16,u32} available in U-Boot tooling:
    + quick and low-line-count
    + [Yamada-san][5]:
      * forbidding u32 for tools is questionable to me
      * Linux kernel and Barebox use {u8,u16,u32} for the tools space
    - breaks U-Boot tradition?
    - has larger impact than [A] and [B]
    - adds type complexity/inconsistency in the tooling space

 D. [Yamada-san] Refactor the headers to minimize the code shared
    between U-Boot space and tooling space:
    + probably the long-term solution
    - high effort
    - can be seen/done as an incremental update on top of [B]

Looking at the above, [B] looks like the natural way to go forward.

[1] https://patchwork.ozlabs.org/patch/1238245/#2363052
[2] commit 7f2531502c ("image: android: Add routine to get dtbo params")
[3] commit c3bfad825a ("image: android: Add functions for handling dtb field")
[4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e6176fa4728fb6d
    ("checkpatch: add --strict warning for c99 fixed size typedefs : int<size>_t")
[5] https://patchwork.ozlabs.org/patch/1238245/#2363340

Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Sam Protsenko <joe.skb7@gmail.com>
Cc: Lokesh Vutla <lokeshvutla@ti.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reported-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Tested-by: Heinrich Schuchardt <xpyron.glpk@gmx.de>

include/image.h

@@ -1416,6 +1416,7 @@ struct cipher_algo *image_get_cipher_algo(const char *full_name);
 #endif /* CONFIG_FIT_VERBOSE */
 #endif /* CONFIG_FIT */
 
+#if !defined(USE_HOSTCC)
 #if defined(CONFIG_ANDROID_BOOT_IMAGE)
 struct andr_img_hdr;
 int android_image_check_header(const struct andr_img_hdr *hdr);
@@ -1437,6 +1438,7 @@ bool android_image_print_dtb_contents(ulong hdr_addr);
 #endif
 
 #endif /* CONFIG_ANDROID_BOOT_IMAGE */
+#endif /* !USE_HOSTCC */
 
 /**
  * board_fit_config_name_match() - Check for a matching board name