drm: Reintroduce drm_kms_free()

drm: Reintroduce drm_kms_free()

* The Linux version of kfree() is a macro with one argument.

* The real kfree() function takes two arguments.

* kfree() cannot be simply called via a function pointer from
  Linux code.

* Re-add the special purpose drm_kms_free() wrapper function
  to handle this situation. It was wrongly removed when drm_crtc.c
  was last synced to Linux.

Reported-by: jh32