powerpc: Remove 83xx from arch/powerpc/platforms/Makefile for now

Since we don't have an 83xx directory or a 83xx/Makefile, having
83xx in causes make clean to fail.
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/platforms/Makefile

@@ -2,7 +2,6 @@ ifeq ($(CONFIG_PPC32),y)
 obj-$(CONFIG_PPC_PMAC)		+= powermac/
 endif
 obj-$(CONFIG_4xx)		+= 4xx/
-obj-$(CONFIG_83xx)		+= 83xx/
 obj-$(CONFIG_85xx)		+= 85xx/
 obj-$(CONFIG_PPC_PSERIES)	+= pseries/
 obj-$(CONFIG_PPC_ISERIES)	+= iseries/