drm: Remove drm_get_format_name()

The %p4cc printk format modifier was recently added to print fourcc codes,
replacing drm_get_format_name(). The function is no longer needed, so
remove it.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210516121315.30321-4-tzimmermann@suse.de