Besides scaling, Arm display scaler also can support image enhancement.
For support it, Add a new property "img_enhancement" to plane, then user
can turn on/off it by this property, and kernel follow user's requirement
to maitain the state and enable/disable the real HW image enhancement.

v2: Rebase and rename "needs_img_enhancement" to "en_img_enhancement"
Signed-off-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>