drm/amd/display: add debugfs disallow edp psr

[Why]
fix reading edp rx crc timeout failure. after
bootup, kernel setup psr with dpcd 0x170 = 5. this
notify rx psr enable and let rx fw start checking crc
for fw internal logic. rx fw may not update crc read
count within dpcd 0x246. read count is always 0. this
will lead tx crc reading timeout.

[How]
add debugfs to let test app to disbable rx crc
checking for rx internal logic. then test app can read
rx crc dpcd 0x246 successfully.
expected app sequence is as below:
1. disable eDP PHY and notify eDP rx with dpcd 0x600 = 2.
2. echo 0x1 /sys/kernel/debug/dri/0/eDP-X/disallow_edp_enter_psr
3. enable eDP PHY and notify eDP rx with dpcd 0x600 = 1 but
   without dpcd 0x170 = 5.
4. read crc from rx dpcd 0x270, 0x246, etc.
5. echo 0x0 /sys/kernel/debug/dri/0/eDP-X/disallow_edp_enter_psr.
   this will let eDP back to normal with psr setup dpcd 0x170 = 5.

Reviewed-by: Wayne Lin <wayne.lin@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>