aarch64: Add support for VMSA feature enhancements.

This patch adds the permission model enhancement and memory
attribute index enhancement features and their corresponding
system registers in AArch64 assembler.
Permission Indirection Extension (FEAT_S1PIE, FEAT_S2PIE)
Permission Overlay Extension (FEAT_S1POE, FEAT_S2POE)
Memory Attribute Index Enhancement (FEAT_AIE)
Extension to Translation Control Registers (FEAT_TCR2)

These features are available by default from Armv9.4-A architecture.