arm64/mm: Add CONFIG_ARM64_PA_BITS_52_[LPA|LPA2]

Going forward, CONFIG_ARM64_PA_BITS_52 could be enabled on a system via two
different architecture features i.e FEAT_LPA for CONFIG_ARM64_64K_PAGES and
FEAT_LPA2 for CONFIG_ARM64_[4K|16K]_PAGES. But CONFIG_ARM64_PA_BITS_52 is
exclussively available on 64K page size config currently, which needs to be
freed up for other page size configs to use when FEAT_LPA2 gets enabled.

To achieve CONFIG_ARM64_PA_BITS_52 and CONFIG_ARM64_64K_PAGES decoupling,
and also to reduce #ifdefs while navigating various page size configs, this
adds two internal config options CONFIG_ARM64_PA_BITS_52_[LPA|LPA2]. While
here it also converts existing 64K page size based FEAT_LPA implementations
to use CONFIG_ARM64_PA_BITS_52_LPA. TTBR representation remains same for
both FEAT_LPA and FEAT_LPA2. No functional change for 64K page size config.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>