powerpc: Make CPU selection logic generic in Makefile

At the time being, when adding a new CPU for selection, both
Kconfig.cputype and Makefile have to be modified.

This patch moves into Kconfig.cputype the name of the CPU to me
passed to the -mcpu= argument.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Rename the option to TARGET_CPU to echo the gcc documentation]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Makefile

@@ -164,13 +164,7 @@ ifdef CONFIG_MPROFILE_KERNEL
 	CC_FLAGS_FTRACE := -pg -mprofile-kernel
 endif
 
-CFLAGS-$(CONFIG_CELL_CPU) += $(call cc-option,-mcpu=cell)
-CFLAGS-$(CONFIG_POWER5_CPU) += $(call cc-option,-mcpu=power5)
-CFLAGS-$(CONFIG_POWER6_CPU) += $(call cc-option,-mcpu=power6)
-CFLAGS-$(CONFIG_POWER7_CPU) += $(call cc-option,-mcpu=power7)
-CFLAGS-$(CONFIG_POWER8_CPU) += $(call cc-option,-mcpu=power8)
-CFLAGS-$(CONFIG_POWER9_CPU) += $(call cc-option,-mcpu=power9)
-CFLAGS-$(CONFIG_PPC_8xx) += $(call cc-option,-mcpu=860)
+CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
 
 # Altivec option not allowed with e500mc64 in GCC.
 ifdef CONFIG_ALTIVEC

arch/powerpc/platforms/Kconfig.cputype

@@ -139,6 +139,21 @@ config E6500_CPU
 
 endchoice
 
+config TARGET_CPU_BOOL
+	bool
+	default !GENERIC_CPU
+
+config TARGET_CPU
+	string
+	depends on TARGET_CPU_BOOL
+	default "cell" if CELL_CPU
+	default "power5" if POWER5_CPU
+	default "power6" if POWER6_CPU
+	default "power7" if POWER7_CPU
+	default "power8" if POWER8_CPU
+	default "power9" if POWER9_CPU
+	default "860" if PPC_8xx
+
 config PPC_BOOK3S
 	def_bool y
 	depends on PPC_BOOK3S_32 || PPC_BOOK3S_64