MIPS: kconfig: globally define CONFIG_SYS_CPU for MIPS

Now the user can select the CPU type for each target. Thus
CONFIG_SYS_CPU could be set globally.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 623ec66..b974e8f 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -4,6 +4,10 @@
 config SYS_ARCH
 	default "mips"
 
+config SYS_CPU
+	default "mips32" if CPU_MIPS32_R1 || CPU_MIPS32_R2
+	default "mips64" if CPU_MIPS64_R1 || CPU_MIPS64_R2
+
 config USE_PRIVATE_LIBGCC
 	default y