drm/amd/display: PSR panel capability debugfs

drm/amd/display: PSR panel capability debugfs

[why]
Adding a debugfs to show PSR capability of the panel and the driver.
To use:
  cat /sys/kernel/debug/dri/0/eDP-X/psr_capability
Expected output:
 Sink support: no/yes
 Driver support: no/yes

[how]
Adding psr_capability to eDP connectors.

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>