Rename arm64_addrenv.c to arm64_addrenv_mmu.c to separate MMU-specific logic.
Add new arm64_addrenv_mpu.c with stub implementations of address environment
functions for MPU-based systems. Enable address environment support in FVP ARMv8-R
Kconfig to support kernel stacks in protected mode. Conditionally build MPU or
MMU address environment code based on CONFIG_ARCH_USE_MMU/CONFIG_ARCH_USE_MPU.
Signed-off-by: hujun5 <hujun5@xiaomi.com>