arch-arm: Add SECURE_RD/WR flags to miscRegInfo

arch-arm: Add SECURE_RD/WR flags to miscRegInfo

The introduction of Secure EL2 in gem5 requires the introduction
of new miscReg flags as there are some EL2 registers which are
accessible from secure mode only

Change-Id: Ib1f0633ed23ea2364670d37c1fefd345ab2363ae
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37615
Tested-by: kokoro <noreply+kokoro@google.com>