MIPS: replace $(CPU) with Kconfig symbols

Conditionally set head-y and lib-y with boolean Kconfig symbols
for selected CPU. This deprecates the usage of the $(CPU) variable.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 363f5ac..d87cbb4 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -167,6 +167,14 @@
 config SUPPORTS_CPU_MIPS64_R2
 	bool
 
+config CPU_MIPS32
+	bool
+	default y if CPU_MIPS32_R1 || CPU_MIPS32_R2
+
+config CPU_MIPS64
+	bool
+	default y if CPU_MIPS64_R1 || CPU_MIPS64_R2
+
 config 32BIT
 	bool