drm/rockchip: vop: fixup linebuffer mode calc error

linebuffer mode should be LB_YUV_3840X5 when width is bigger than 1280
in yuv mode.

Separate yuv and rgb case makes the scl_vop_cal_lb_mode() logic clearer.

Signed-off-by: Sandy Huang <hjc@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1530001004-25036-1-git-send-email-hjc@rock-chips.com