media: platform: Aspeed: Make reserved memory optional

Reserved memory doesn't need to be required; system memory would work
fine.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>