powerpc/64s: Move CPU -mtune options into Kconfig

Currently the -mtune options are set in the Makefile, depending on what
the compiler supports.

One downside of doing it that way is that the chosen -mtune option is
not recorded in the .config.

Another downside is that if there's ever a need to do more complicated
logic to calculate the correct option, that gets messy in the Makefile.

So move the determination of which -mtune option to use into Kconfig
logic.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230329234308.2215833-1-mpe@ellerman.id.au

Author: mpe

arch/powerpc/Makefile

@@ -157,9 +157,7 @@ endif
 CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
 AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
 
-CFLAGS-$(CONFIG_POWERPC64_CPU) += $(call cc-option,-mtune=power10,	\
-				  $(call cc-option,-mtune=power9,	\
-				  $(call cc-option,-mtune=power8)))
+CFLAGS-y += $(CONFIG_TUNE_CPU)
 
 asinstr := $(call as-instr,lis 9$(comma)foo@high,-DHAVE_AS_ATHIGH=1)
 

arch/powerpc/platforms/Kconfig.cputype

@@ -275,6 +275,13 @@ config TARGET_CPU
 	default "e500mc" if E500MC_CPU
 	default "powerpc" if POWERPC_CPU
 
+config TUNE_CPU
+	string
+	depends on POWERPC64_CPU
+	default "-mtune=power10" if $(cc-option,-mtune=power10)
+	default "-mtune=power9"  if $(cc-option,-mtune=power9)
+	default "-mtune=power8"  if $(cc-option,-mtune=power8)
+
 config PPC_BOOK3S
 	def_bool y
 	depends on PPC_BOOK3S_32 || PPC_BOOK3S_64