drm: Switch to %p4cc format modifier

Switch DRM drivers from drm_get_format_name() to %p4cc. This gets rid of a
large number of temporary variables at the same time.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210216155723.17109-4-sakari.ailus@linux.intel.com