mem-ruby: Use Packet writing functions instead of memcpy

mem-ruby: Use Packet writing functions instead of memcpy

Classes were using memcpy instead of the Packet functions
created for writing to/from the packet. This allows these
writes to be better checked and tracked.

Change-Id: Iae3fba1351330916ee1d4103809c71e151b1639e
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/13915
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>