After the kernel 4.4, the DRM disable flow was changed, if DPI was
disableed before CRTC, it will cause warning message as following:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 1339 at ../../linux/linux-4.4.24-mtk/drivers/gpu/drm/drm_irq.c:1326 drm_wait_one_vblank+0x188/0x18c()
vblank wait timed out on crtc 0
Modules linked in: bridge mt8521p_ir_shim(O) i2c_eeprom(O) mtk_m4(O) fuse_ctrl(O) virtual_block(O) caamkeys(PO) chk(PO) amperctl(O) ledctl(O) apple_auth(PO) micctl(O) sensors(PO) lla(O) sdd(PO) ice40_fpga(O) psmon(O) event_queue(PO) utils(O) blackbox(O)
CPU: 0 PID: 1339 Comm: kworker/0:1 Tainted: P        W  O    4.4.24 #1
Hardware name: Mediatek Cortex-A7 (Device Tree)
Workqueue: events drm_mode_rmfb_work_fn
[<c001a710>] (unwind_backtrace) from [<c00151e4>] (show_stack+0x20/0x24)
[<c00151e4>] (show_stack) from [<c027961c>] (dump_stack+0x98/0xac)
[<c027961c>] (dump_stack) from [<c002ac54>] (warn_slowpath_common+0x94/0xc4)
[<c002ac54>] (warn_slowpath_common) from [<c002acc4>] (warn_slowpath_fmt+0x40/0x48)
[<c002acc4>] (warn_slowpath_fmt) from [<c03307ac>] (drm_wait_one_vblank+0x188/0x18c)
[<c03307ac>] (drm_wait_one_vblank) from [<c03307d8>] (drm_crtc_wait_one_vblank+0x28/0x2c)
[<c03307d8>] (drm_crtc_wait_one_vblank) from [<c034f48c>] (mtk_drm_crtc_disable+0x78/0x240)
[<c034f48c>] (mtk_drm_crtc_disable) from [<c03240d4>] (drm_atomic_helper_commit_modeset_disables+0x128/0x3b8)
[<c03240d4>] (drm_atomic_helper_commit_modeset_disables) from [<c0350a7c>] (mtk_atomic_complete+0x74/0xb4)
[<c0350a7c>] (mtk_atomic_complete) from [<c0350b24>] (mtk_atomic_commit+0x68/0x98)
[<c0350b24>] (mtk_atomic_commit) from [<c034ab48>] (drm_atomic_commit+0x54/0x74)
[<c034ab48>] (drm_atomic_commit) from [<c0325c4c>] (drm_atomic_helper_set_config+0x7c/0xa0)
[<c0325c4c>] (drm_atomic_helper_set_config) from [<c0338594>] (drm_mode_set_config_internal+0x68/0xe4)
[<c0338594>] (drm_mode_set_config_internal) from [<c033967c>] (drm_framebuffer_remove+0xe4/0x120)
[<c033967c>] (drm_framebuffer_remove) from [<c0339700>] (drm_mode_rmfb_work_fn+0x48/0x58)
[<c0339700>] (drm_mode_rmfb_work_fn) from [<c0043a38>] (process_one_work+0x154/0x50c)
[<c0043a38>] (process_one_work) from [<c0044074>] (worker_thread+0x284/0x568)
[<c0044074>] (worker_thread) from [<c0049dc4>] (kthread+0xec/0x104)
[<c0049dc4>] (kthread) from [<c0010678>] (ret_from_fork+0x14/0x3c)
---[ end trace 12ae5358e992abd5 ]---

so, we add refcount for DPI power on/off to protect the flow.
Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Signed-off-by: chunhui dai <chunhui.dai@mediatek.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>