drm/print: Add generic drm dev printk function

drm/print: Add generic drm dev printk function

We already have some drm printk functions that need to duplicate
a code to get a similar format of the final result, for example:

  [ ] 0000:00:00.0: [drm:foo] bar
  [ ] 0000:00:00.0: [drm] foo bar
  [ ] 0000:00:00.0: [drm] *ERROR* foo

Add a generic __drm_dev_vprintk() function that can format the
final message like all other existing function do and allows us
to keep the formatting code in one place.

Cc: Jani Nikula <[email protected]>
Signed-off-by: Michal Wajdeczko <[email protected]>
Reviewed-by: Jani Nikula <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Rodrigo Vivi <[email protected]>