drm: shmobile: Use %p4cc to print fourcc codes

Replace the printing of hexadecimal fourcc format codes by
pretty-printed format names, using the "%p4cc" format specifier.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1a63e5afc8a85f7ae10f7f4395c2d065ba1aeb59.1684854992.git.geert+renesas@glider.be