plat/arm: Migrate to new interfaces

- Remove references to removed build options.
- Remove support for legacy GIC driver.
- Remove support for LOAD_IMAGE_V2=0.

Change-Id: I72f8c05620bdf4a682765e6e53e2c04ca749a3d5
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
15 files changed