powerpc/32s: Rename head_32.S to head_book3s_32.S

Unlike PPC64 which had a single head_64.S, PPC32 are multiple ones.
There is the head_32.S, selected by default based on the value of BITS
and overridden based on some CONFIG_ values. This leads to thinking
that it may be selected by different types of PPC32 platform but
indeed it ends up being selected by book3s/32 only.

Make that explicit by:
- Not doing any default selection based on BITS.
- Renaming head_32.S to head_book3s_32.S.
- Get head_book3s_32.S selected only by CONFIG_PPC_BOOK3S_32.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Fix head_$(BITS).o reference in arch/powerpc/Makefile]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/319d379f696412681c66a987cc75e6abf8f958d2.1601975100.git.christophe.leroy@csgroup.eu

arch/powerpc/Makefile

@@ -264,7 +264,8 @@ KBUILD_CFLAGS += $(cpu-as-y)
 KBUILD_AFLAGS += $(aflags-y)
 KBUILD_CFLAGS += $(cflags-y)
 
-head-y				:= arch/powerpc/kernel/head_$(BITS).o
+head-$(CONFIG_PPC64)		:= arch/powerpc/kernel/head_64.o
+head-$(CONFIG_PPC_BOOK3S_32)	:= arch/powerpc/kernel/head_book3s_32.o
 head-$(CONFIG_PPC_8xx)		:= arch/powerpc/kernel/head_8xx.o
 head-$(CONFIG_40x)		:= arch/powerpc/kernel/head_40x.o
 head-$(CONFIG_44x)		:= arch/powerpc/kernel/head_44x.o

arch/powerpc/kernel/Makefile

@@ -95,7 +95,8 @@ 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_$(BITS).o
+extra-$(CONFIG_PPC64)		:= head_64.o
+extra-$(CONFIG_PPC_BOOK3S_32)	:= head_book3s_32.o
 extra-$(CONFIG_40x)		:= head_40x.o
 extra-$(CONFIG_44x)		:= head_44x.o
 extra-$(CONFIG_FSL_BOOKE)	:= head_fsl_booke.o

arch/powerpc/kernel/head_32.S → arch/powerpc/kernel/head_book3s_32.S

@@ -50,7 +50,7 @@
 
 	__HEAD
 	.stabs	"arch/powerpc/kernel/",N_SO,0,0,0f
-	.stabs	"head_32.S",N_SO,0,0,0f
+	.stabs	"head_book3s_32.S",N_SO,0,0,0f
 0:
 _ENTRY(_stext);