arch-arm: AArch64 reg access HCR_EL2.E2H filter

arch-arm: AArch64 reg access HCR_EL2.E2H filter

Some AArch64 system registers report UNDEFINED behaviours if accessed
from EL2 or EL3 in a non-EL2 Host enabled (HCR_EL2.E2H == 0) environment.
Examples of these are seen in the Generic Timer system registers,
namely CNTP_CTL_EL02 or CNTKCTL_EL12.
This patch provides an ISA filter for specifying the above condition.

Change-Id: I240f9afdb000faf5d3c9274ba12bd4cc41fe8604
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24664
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>