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/docs/components/granule-protection-tables-design.rst b/docs/components/granule-protection-tables-design.rst
index 7a4ffcf..9d85bef 100644
--- a/docs/components/granule-protection-tables-design.rst
+++ b/docs/components/granule-protection-tables-design.rst
@@ -81,7 +81,7 @@
 
 In the reference implementation for FVP models, you can find an example of PAS
 region definitions in the file ``plat/arm/board/fvp/include/fvp_pas_def.h``.
-Table creation API calls can be found in ``plat/arm/common/arm_bl2_setup.c`` and
+Table creation API calls can be found in ``plat/arm/common/arm_common.c`` and
 runtime initialization API calls can be seen in
 ``plat/arm/common/arm_bl31_setup.c``.