physmem: disallow direct access to RAM DEVICE in address_space_write_rom()

physmem: disallow direct access to RAM DEVICE in address_space_write_rom()

As documented in commit 4a2e242bbb306 ("memory: Don't use memcpy for
ram_device regions"), we disallow direct access to RAM DEVICE regions.

This change implies that address_space_write_rom() and
cpu_memory_rw_debug() won't be able to write to RAM DEVICE regions. It
will also affect cpu_flush_icache_range(), but it's only used by
hw/core/loader.c after writing to ROM, so it is expected to not apply
here with RAM DEVICE.

This fixes direct access to these regions where we don't want direct
access. We'll extend cpu_memory_rw_debug() next to also be able to write to
these (and IO) regions.

This is a preparation for further changes.

Cc: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20250210084648.33798-5-david@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>