KVM: selftests: arm64: Support P52V48 4K and 16K guest_modes

Add support for VM_MODE_P52V48_4K and VM_MODE_P52V48_16K guest modes by
using the FEAT_LPA2 pte format for stage1, when FEAT_LPA2 is available.

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