MIPS: SEAD3 can support MIPS32r6 CPUs

There are CPUs/bitfiles available for use with SEAD3 boards which
implement release 6 of the MIPS architecture. Allow building the kernel
for such a system.

Signed-off-by: Paul Burton <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/12372/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/Kconfig

···
 	select MIPS_MSC
 	select SYS_HAS_CPU_MIPS32_R1
 	select SYS_HAS_CPU_MIPS32_R2
+	select SYS_HAS_CPU_MIPS32_R6
 	select SYS_HAS_CPU_MIPS64_R1
 	select SYS_HAS_EARLY_PRINTK
 	select SYS_SUPPORTS_32BIT_KERNEL