KVM: arm64: Use LPA2 page-tables for hyp stage1 if HW supports it

Implement a simple policy whereby if the HW supports FEAT_LPA2 for the
page size we are using, always use LPA2-style page-tables for hyp stage
1, regardless of the IPA or PA size requirements. When in use we can now
support up to 52-bit IPA and PA sizes.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>