mediatek: Migrate to new interfaces

mediatek: Migrate to new interfaces

- mt6795: Migrate to new GIC interfaces.
- Remove support for PSCI platform compatibility layer.
- Migrate to bl31_early_platform_setup2().
- Migrate from cm_init_context() to cm_init_my_context().
- Use PLAT_VIRT_ADDR_SPACE_SIZE and PLAT_PHY_ADDR_SPACE_SIZE.
- Update Makefile paths.
- Use private definition of bl31_params_t.

This is an incomplete migration, mt6795 doesn't currently compile.

Change-Id: Icf9307637066cd6f2166524715e4f117f5ce2350
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>