MSCC: add support for Luton SoCs

As the Ocelots SoCs, this family of SoCs are found in the Microsemi
Switches solution.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
diff --git a/arch/mips/mach-mscc/Kconfig b/arch/mips/mach-mscc/Kconfig
index 7f1b270..a8cace0 100644
--- a/arch/mips/mach-mscc/Kconfig
+++ b/arch/mips/mach-mscc/Kconfig
@@ -21,6 +21,12 @@
 	help
 	  This supports MSCC Ocelot family of SOCs.
 
+config SOC_LUTON
+	bool
+	select SOC_VCOREIII
+	help
+	  This supports MSCC Luton family of SOCs.
+
 config SYS_CONFIG_NAME
 	default "vcoreiii"
 
@@ -41,6 +47,13 @@
 	  When selected, CONFIG_DEFAULT_DEVICE_TREE should be set to
 	  ocelot_pcb123
 
+config TARGET_LUTON_PCB091
+	bool "MSCC PCB091 Reference Board"
+	select SOC_LUTON
+	select MSCC_BITBANG_SPI_GPIO
+	help
+	  When selected, CONFIG_DEFAULT_DEVICE_TREE should be set to
+	  luton_pcb091
 endchoice
 
 choice