boston: Pad binary in .mcs to a multiple of 16 bytes

When flashing U-Boot on a Boston board using Xilinx Vivado tools, the
final 0x00 byte which ends the .relocs section seems to be skipped &
left in flash as 0xff unless the data contained in the .mcs is padded
out to a 16 byte boundary. Without our final zero byte relocation will
fail with an error about a spurious reloc:

Avoid this problem by padding out the data in the .mcs file to a 16 byte
boundary using srec_cat's -range-pad functionality.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

board/imgtec/boston/config.mk

@@ -3,7 +3,10 @@
 #
 
 quiet_cmd_srec_cat = SRECCAT $@
-      cmd_srec_cat = srec_cat -output $@ -$2 $< -binary -offset $3
+      cmd_srec_cat = srec_cat -output $@ -$2 \
+			$< -binary \
+			-fill 0x00 -within $< -binary -range-pad 16 \
+			-offset $3
 
 u-boot.mcs: u-boot.bin
 	$(call cmd,srec_cat,intel,0x7c00000)