powerpc/44x: Simplify CONFIG_44x checks in Makefile

The entire 44x directory is omitted if CONFIG_44x is not enabled, so
within the 44x/Makefile CONFIG_44x is always y. So convert
obj-$(CONFIG_44x) to the more obvious obj-y.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/44x/Makefile

-obj-$(CONFIG_44x)	+= misc_44x.o
+obj-y	+= misc_44x.o
 ifneq ($(CONFIG_PPC4xx_CPM),y)
-obj-$(CONFIG_44x)	+= idle.o
+obj-y	+= idle.o
 endif
 obj-$(CONFIG_PPC44x_SIMPLE) += ppc44x_simple.o
 obj-$(CONFIG_EBONY)	+= ebony.o