powerpc: Don't compile in arch/ppc/kernel for 32-bit ARCH=powerpc

All of the things needed for 32-bit ARCH=powerpc builds have now
moved to arch/powerpc/kernel, so we don't need to go down into
arch/ppc/kernel any more, and we can remove the CONFIG_PPC_MERGE
conditional from arch/ppc/kernel/Makefile.

There were two files still referenced in the merge section of
arch/ppc/kernel/Makefile: ppc-stub.o, depending on CONFIG_KGDB,
and dma-mapping.o, depending on CONFIG_NOT_COHERENT_CACHE. None
of the platforms currently in ARCH=powerpc have caches that
aren't coherent with DMA, but when we do get one we'll move
dma-mapping.c over. As for CONFIG_KGDB, none of the Kconfig
files in the tree define it, so I'll let it languish for now.

Signed-off-by: Paul Mackerras <[e-mail]>

arch/powerpc/Makefile

···
 				   arch/powerpc/lib/ \
 				   arch/powerpc/sysdev/ \
 				   arch/powerpc/platforms/
-core-$(CONFIG_PPC32)		+= arch/ppc/kernel/
 core-$(CONFIG_MATH_EMULATION)	+= arch/ppc/math-emu/
 core-$(CONFIG_XMON)		+= arch/powerpc/xmon/
 core-$(CONFIG_APUS)		+= arch/ppc/amiga/

arch/ppc/kernel/Makefile

···
 #
 # Makefile for the linux kernel.
 #
-ifneq ($(CONFIG_PPC_MERGE),y)
-
 extra-$(CONFIG_PPC_STD_MMU)	:= head.o
 extra-$(CONFIG_40x)		:= head_4xx.o
 extra-$(CONFIG_44x)		:= head_44x.o
···
 
 ifndef CONFIG_MATH_EMULATION
 obj-$(CONFIG_8xx)		+= softemu8xx.o
-endif
-
-# These are here while we do the architecture merge
-
-else
-obj-$(CONFIG_NOT_COHERENT_CACHE)	+= dma-mapping.o
-obj-$(CONFIG_KGDB)		+= ppc-stub.o
 endif