arch, arm: Print value being ignored on DummyISA write

arch, arm: Print value being ignored on DummyISA write

When ignoring writes to the Dummy ISA device (DummyISADevice),
additionally print the value being ignored in the diagnostic.

Sometimes it is useful to know exactly what we are dropping ...

Change-Id: I9a01623611f0da0aa12b065fbb2031aa27e2c036
Signed-off-by: Sean McGoogan <Sean.McGoogan@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5731
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>