feat(gpt): add ci support to test using backup-gpt

Current GPT test uses the primary GPT header, so corrupt primary GPT
header at second LBA after the MBR. This would force it to use the
backup-gpt header at last LBA.

Also additional changes done to handle backup_gpt header to TF-A
causes BL31 to run out of space so add FVP_TRUSTED_SRAM_SIZE=384
to gpt builds.

Change-Id: I6660a5e3c533f58738272302c8008c88dd82b8a6
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/tf_config/fvp-gpt b/tf_config/fvp-gpt
index 0572149..ee5c35e 100644
--- a/tf_config/fvp-gpt
+++ b/tf_config/fvp-gpt
@@ -1,3 +1,4 @@
 ARM_GPT_SUPPORT=1
 CROSS_COMPILE=aarch64-none-elf-
 PLAT=fvp
+FVP_TRUSTED_SRAM_SIZE=384