ARM: BCM5301X: Enable SPI-NOR on dual flash devices

Commit 1b47b98a ("ARM: BCM5301X: Add DT entry for SPI controller and
NOR flash") enabled SPI-NOR device on routers using serial flash only.
However there are also devices with two flash memories:
1) Small SPI attached flash used mostly for booting
2) Bigger NAND used mostly for storing firmware
On such devices we still need SPI-NOR e.g. to access NVRAM data.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>