rockchip/rga: add rga flush data cache

rockchip/rga: add rga flush data cache

If the buffer alloced from the ion, user can flush
it by ion apis, but if the buffer was alloced by
other apis like malloc, user space is not easy to
flush the data cache. So rga flush the data cache
for cache coherence.

Change-Id: I5fcfc3e00c6a8f6b12ed66043b37b0c7c840e7ee
Signed-off-by: Zikim,Wei <wzq@rock-chips.com>