Change remoteproc to map ROM as device memory

The ROM is memory attached to the remote processor and should be mapped
as device memory rather than normal memory to ensure memory transactions
are handled correctly. To ensure this, the remoteproc driver will now
map the ROM as device memory.

Change-Id: I1b5f1dcd7af06bb9e1656f653d65813f7af424c3
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>