xlat v2: Introduce xlat granule size helpers

The function xlat_arch_is_granule_size_supported() can be used to check
if a specific granule size is supported. In Armv8, AArch32 only supports
4 KiB pages. AArch64 supports 4 KiB, 16 KiB or 64 KiB depending on the
implementation, which is detected at runtime.

The function xlat_arch_get_max_supported_granule_size() returns the max
granule size supported by the implementation.

Even though right now they are only used by SPM, they may be useful in
other places in the future. This patch moves the code currently in SPM
to the xlat tables lib so that it can be reused.

Change-Id: If54624a5ecf20b9b9b7f38861b56383a03bbc8a4
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>