arm: add ALL_PLAT, QEMU, Rcar3 and MPSoC configs

arm: add ALL_PLAT, QEMU, Rcar3 and MPSoC configs

Add a "Platform Support" choice with four kconfig options: QEMU, RCAR3,
MPSOC and ALL_PLAT. They enable the required options for their hardware
platform. ALL_PLAT enables all available platforms and it's the default.
It doesn't automatically select any of the related drivers, otherwise
they cannot be disabled. ALL_PLAT is implemented by using hidden options
with default values depending on ALL_PLAT.

In the case of the MPSOC that has a platform file under
arch/arm/platforms/, build the file if MPSOC.

Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
CC: artem_mygaiev@epam.com
CC: volodymyr_babchuk@epam.com
---
Changes in v8:
- remove QEMU_PLATFORM and RCAR3_PLATFORM that are currently unused
- remove selects from ALL
- rename ALL to ALL_PLAT
- introduce ALL64_PLAT and ALL32_PLAT

Changes in v5:
- turn platform support into a choice
- add ALL

Changes in v4:
- fix GICv3/GICV3
- default y to all options
- build xilinx-zynqmp if MPSOC