media: aspeed: add AST2600 support

Video engine in AST2600 has the exactly same register set with
AST2500 except VR084 register which provides more precise JPEG
size read back. This commit adds support for the difference and
adds 'aspeed,ast2600-video-engine' compatible OF string.

Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>