exynos: add g2d_scale_and_blend

This is a combination of g2d_copy_with_scale and g2d_scale.
It is a pretty common operation to scale one buffer and then
blend it on top of another, so provide a direct way to that
operation.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Reviewed-by: Inki Dae <inki.dae@samsung.com>
Tested-by: Joonyoung Shim <jy0922.shim@samsung.com>