mem: Allow packet to provide its own addr range

mem: Allow packet to provide its own addr range

Add a getter to Packet to allow it to provide its own addr
range.

Change-Id: I2128ea3b71906502d10d9376b050a62407defd23
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17536
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>