media: staging: imgu: make imgu work on low frequency for low input

Currently, imgu is working on 450MHz for all cases, however
in some cases (input frame less than 2048x1152), the imgu
did not need work in high frequency.
This patch make imgu work on 200MHz if the imgu input
frame is less than 2048x1152 to save power.

Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>