drm/rockchip: vop: add rk3126 vop support

RK3126 vop register layout is similar with rk3036, so some feature
can reuse with rk3036.

RK3126 support two overlay plane and one hwc plane, max output
resolution is 1080p. it support IOMMU, and its IOMMU same as
rk3288's

Signed-off-by: Sandy Huang <hjc@rock-chips.com>
Reviewed-by: Mark Yao <mark.yao@rock-chips.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1510658857-90299-1-git-send-email-hjc@rock-chips.com