MIPS: BMIPS: Add support SPI device nodes

Adds SPI device nodes to BCM7xxx MIPS based SoCs.

Signed-off-by: Jaedon Shin <jaedon.shin@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14990/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/boot/dts/brcm/bcm97420c.dts

@@ -79,3 +79,7 @@
 &ohci1 {
 	status = "okay";
 };
+
+&mspi {
+	status = "okay";
+};