powerpc: Add ppc32_allmodconfig defconfig target

Because the allmodconfig logic just sets every symbol to M or Y, it
has the effect of always generating a 64-bit config, because
CONFIG_PPC64 becomes Y.

So to make it easier for folks to test 32-bit code, provide a phony
defconfig target that generates a 32-bit allmodconfig.

The 32-bit port has several mutually exclusive CPU types, we choose
the Book3S variants as that's what the help text in Kconfig says is
most common.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Makefile

@@ -354,6 +354,11 @@ mpc86xx_smp_defconfig:
 	$(call merge_into_defconfig,mpc86xx_basic_defconfig,\
 		86xx-smp 86xx-hw fsl-emb-nonhw)
 
+PHONY += ppc32_allmodconfig
+ppc32_allmodconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/book3s_32.config \
+		-f $(srctree)/Makefile allmodconfig
+
 define archhelp
   @echo '* zImage          - Build default images selected by kernel config'
   @echo '  zImage.*        - Compressed kernel image (arch/$(ARCH)/boot/zImage.*)'

arch/powerpc/configs/book3s_32.config

@@ -0,0 +1,2 @@
+CONFIG_PPC64=n
+CONFIG_PPC_BOOK3S_32=y