feat(arm): move GPT setup to common BL source

As of now, GPT setup is being handled from BL2 for plat/arm platforms.
However, for platforms having a separate entity to load firmware images,
it is possible for BL31 to setup the GPT. In order to address this
concern, move the GPT setup implementation from arm_bl2_setup.c file to
arm_common.c. Additionally, rename the API from arm_bl2_gpt_setup to
arm_gpt_setup to make it boot stage agnostic.

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: I35d17a179c8746945c69db37fd23d763a7774ddc
diff --git a/include/plat/arm/common/plat_arm.h b/include/plat/arm/common/plat_arm.h
index 97f5446..4c425a7 100644
--- a/include/plat/arm/common/plat_arm.h
+++ b/include/plat/arm/common/plat_arm.h
@@ -375,6 +375,7 @@
 const mmap_region_t *plat_arm_get_mmap(void);
 
 const arm_gpt_info_t *plat_arm_get_gpt_info(void);
+void arm_gpt_setup(void);
 
 /* Allow platform to override psci_pm_ops during runtime */
 const plat_psci_ops_t *plat_arm_psci_override_pm_ops(plat_psci_ops_t *ops);