doc: arch: sandbox: Replace all the instances of README.sandbox

commit 49116e6d23 ("doc: arch: Convert README.sandbox to reST")
Moves README.sandbox to doc/arch.
Replace all the existing instances to point to the right documentation
file.

Signed-off-by: Keerthy <j-keerthy@ti.com>

README

@@ -212,7 +212,7 @@ board. This allows feature development which is not board- or architecture-
 specific to be undertaken on a native platform. The sandbox is also used to
 run some of U-Boot's tests.
 
-See board/sandbox/README.sandbox for more details.
+See doc/arch/index.rst for more details.
 
 
 Board Initialisation Flow:

arch/sandbox/include/asm/spi.h

@@ -1,5 +1,5 @@
 /*
- * Simulate a SPI port and clients (see README.sandbox for details)
+ * Simulate a SPI port and clients (see doc/arch/sandbox.rst for details)
  *
  * Copyright (c) 2011-2013 The Chromium OS Authors.
  * See file CREDITS for list of people who contributed to this

doc/README.gpt

@@ -229,7 +229,7 @@ U-BOOT> gpt rename mmc 0 1 primary
 
 The GPT functionality may be tested with the 'sandbox' board by
 creating a disk image as described under 'Block Device Emulation' in
-board/sandbox/README.sandbox:
+doc/arch/index.rst:
 
 =>host bind 0 ./disk.raw
 => gpt read host 0

drivers/net/Kconfig

@@ -196,7 +196,7 @@ config ETH_SANDBOX_RAW
 	  This driver is a bridge from the bottom of the network stack
 	  in U-Boot to the RAW AF_PACKET API in Linux. This allows real
 	  network traffic to be tested from within sandbox. See
-	  board/sandbox/README.sandbox for more details.
+	  doc/arch/index.rst for more details.
 
 config ETH_DESIGNWARE
 	bool "Synopsys Designware Ethernet MAC"