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_sw.c b/libfdt/fdt_sw.c
index df09876..92f8f0b 100644
--- a/libfdt/fdt_sw.c
+++ b/libfdt/fdt_sw.c
@@ -121,7 +121,7 @@
 	if ((offset + sizeof(*re)) > fdt_totalsize(fdt))
 		return -FDT_ERR_NOSPACE;
 
-	re = (struct fdt_reserve_entry *)(fdt + offset);
+	re = (struct fdt_reserve_entry *)((char *)fdt + offset);
 	re->address = cpu_to_fdt64(addr);
 	re->size = cpu_to_fdt64(size);