Since the drm atomic framework, only a small part of the vop
register needs sync write, Currently seems only following registers
need sync write:
   cfg_done, standby and interrupt related register.

All ctrl registers are using the sync write method that is
inefficient, hardcode the write_relaxed flags to vop registers,
then can only do synchronize write for those actual needed register.
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1501049953-5946-1-git-send-email-mark.yao@rock-chips.com