MIPS: BCM63xx: Make board setup code register the spi platform device

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: grant.likely@secretlab.ca
Cc: spi-devel-general@lists.sourceforge.net
Patchwork: https://patchwork.linux-mips.org/patch/3317/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>