malta: Support MIPS32r6 configurations

Both real Malta boards & QEMU's Malta emulation can feature MIPS32r6
CPUs. Allow building U-Boot for such systems by selecting
CONFIG_SUPPORTS_CPU_MIPS32_R6 for Malta.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 994168c..dc34c18 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -28,6 +28,7 @@
 	select SUPPORTS_LITTLE_ENDIAN
 	select SUPPORTS_CPU_MIPS32_R1
 	select SUPPORTS_CPU_MIPS32_R2
+	select SUPPORTS_CPU_MIPS32_R6
 	select SWAP_IO_SPACE
 	select MIPS_L1_CACHE_SHIFT_6