aarch64: Add support to new features in RAS extension.

This patch also adds support for:
1. FEAT_RASv2 feature and "ERXGSR_EL1" system register.
RASv2 feature is enabled by passing +rasv2 to -march
(eg: -march=armv8-a+rasv2).

2. FEAT_SCTLR2 and following system registers.
SCTLR2_EL1, SCTLR2_EL12, SCTLR2_EL2 and SCTLR2_EL3.

3. FEAT_FGT2 and following system registers.
HDFGRTR2_EL2, HDFGWTR2_EL2, HFGRTR2_EL2, HFGWTR2_EL2

4. FEAT_PFAR and following system registers.
PFAR_EL1, PFAR_EL2 and PFAR_EL12.

FEAT_RASv2, FEAT_SCTLR2, FEAT_FGT2 and FEAT_PFAR features are by default
enabled from Armv9.4-A architecture.

This patch also adds support for two read only system registers
id_aa64mmfr3_el1 and id_aa64mmfr4_el1, which are available from
Armv8-A Architecture.