arch-arm: Add support for secure state in semihosting

arch-arm: Add support for secure state in semihosting

The semihosting component currently issues non-secure memory accesses
using the standard port proxy. This doesn't work when the guest is
running in secure state.

Change-Id: Id34b142cfcd9d77b455c040ae7f7397c29aebbc6
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jack Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/8365
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>