MIPS: BCM63xx: Define BCM6358 SPI base address

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/3315/


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