dev-arm: Allow 32 bit accesses to GITS_C(WRITER/READR/BASER)

dev-arm: Allow 32 bit accesses to GITS_C(WRITER/READR/BASER)

For those registers (GITS_CWRITER, GITS_READR and GITS_CBASER)
Bits [63:32] and bits [31:0] are accessible separately.

Change-Id: Ibf60b5e4fd20efb21a63570e6012862e37946877
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20256
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>