dtc: Enable and fix -Wpointer-arith warnings

This patch turns on the -Wpointer-arith option in the dtc Makefile,
and fixes the resulting warnings due to using (void *) in pointer
arithmetic.  While convenient, pointer arithmetic on void * is not
portable, so it's better that we avoid it, particularly in libfdt.

Also add necessary definition of uintptr_t needed by David Gibson's
changeset "dtc: Enable and fix -Wpointer-arith warnings" (the definition
comes from stdint.h, which u-boot doesn't have). -- gvb

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Gerald Van Baren <vanbaren@cideas.com>
diff --git a/libfdt/fdt_wip.c b/libfdt/fdt_wip.c
index 24e1724..b336113 100644
--- a/libfdt/fdt_wip.c
+++ b/libfdt/fdt_wip.c
@@ -80,7 +80,7 @@
 {
 	uint32_t *p;
 
-	for (p = start; (void *)p < (start + len); p++)
+	for (p = start; (char *)p < ((char *)start + len); p++)
 		*p = cpu_to_fdt32(FDT_NOP);
 }