refactor: convert arm platforms to use the generic GIC driver

This reduces the code the platforms have to carry and makes their build
rules a bit simpler.

The main benefit is that plat_my_core_pos() no longer needs to be called
within the driver, helping with performance a bit.

Change-Id: I0b0d1d36d20d67c41c8c9dc14ade11bda6d4a6af
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
30 files changed