dev-arm: Fix GICv3 IGRPMOD writes
dev-arm: Fix GICv3 IGRPMOD writes

Writes to IGRPMOD were not right shifting the value, which resulted in
interrupts having a IGRPMOD value > 1, whereas the only allowed values
are 0 and 1.

Change-Id: Id491bd1b184d6e5abeeea25ea272eeb91792ccf7
Signed-off-by: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Reviewed-by: Andreas Sandberg <c9f5686ee5bd561c93f9de79681eee75bfa7f36e@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20613
Maintainer: Andreas Sandberg <c9f5686ee5bd561c93f9de79681eee75bfa7f36e@arm.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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