In both the AArch32 and AArch64 versions, this function used to check
the sanity of the PLAT_PHY_ADDR_SPACE_SIZE in regard to the
architectural maximum value. Instead, export the
xlat_arch_get_max_supported_pa() function and move the debug
assertion in AArch-agnostic code.

The AArch64 used to also precalculate the TCR.PS field value, based
on the size of the physical address space. This is now done directly
by enable_mmu_arch(), which now receives the physical address space size
in argument.

Change-Id: Ie77ea92eb06db586f28784fdb479c6e27dd1acc1
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>