ARM: shmobile: sh73a0 pinmux platform device cleanup

Use DEFINE_RES_MEM() and platform_device_register_simple()
to save a couple of lines of code.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
[ remove const from resource pfc_resources to avoid section miss-match
  reported by 4.4.5 ]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>