powerpc: Update Kconfig + Makefile to prepare for server doorbells

Move the rule to build doorbell support out of the Makefile and into a
new Kconfig boolean that platforms can select.

We will add doorbell support to pseries as well in the next patch.

Signed-off-by: Ian Munsie <[e-mail]>
Tested-by: Michael Neuling <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/kernel/Makefile

···
 obj64-$(CONFIG_HIBERNATION)	+= swsusp_asm64.o
 obj-$(CONFIG_MODULES)		+= module.o module_$(CONFIG_WORD_SIZE).o
 obj-$(CONFIG_44x)		+= cpu_setup_44x.o
-obj-$(CONFIG_PPC_FSL_BOOK3E)	+= cpu_setup_fsl_booke.o dbell.o
-obj-$(CONFIG_PPC_BOOK3E_64)	+= dbell.o
+obj-$(CONFIG_PPC_FSL_BOOK3E)	+= cpu_setup_fsl_booke.o
+obj-$(CONFIG_PPC_DOORBELL)	+= dbell.o
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
 
 extra-y				:= head_$(CONFIG_WORD_SIZE).o

arch/powerpc/platforms/Kconfig.cputype

···
 	bool "Embedded processors"
 	select PPC_FPU # Make it a choice ?
 	select PPC_SMP_MUXED_IPI
+	select PPC_DOORBELL
 
 endchoice
 
···
 	select FSL_EMB_PERFMON
 	select PPC_SMP_MUXED_IPI
 	select SYS_SUPPORTS_HUGETLBFS if PHYS_64BIT || PPC64
+	select PPC_DOORBELL
 	default y if FSL_BOOKE
 
 config PTE_64BIT
···
 
 config CHECK_CACHE_COHERENCY
 	bool
+
+config PPC_DOORBELL
+	bool
+	default n
 
 endmenu