dtc: Enable and fix -Wcast-qual warnings

Enabling -Wcast-qual warnings in dtc shows up a number of places where
we are incorrectly discarding a const qualification.  There are also
some places where we are intentionally discarding the 'const', and we
need an ugly cast through uintptr_t to suppress the warning.  However,
most of these are pretty well isolated with the *_w() functions.  So
in the interests of maximum safety with const qualifications, this
patch enables the warnings and fixes the existing complaints.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Gerald Van Baren <vanbaren@cideas.com>
diff --git a/libfdt/fdt_rw.c b/libfdt/fdt_rw.c
index 4a16014..6837fb1 100644
--- a/libfdt/fdt_rw.c
+++ b/libfdt/fdt_rw.c
@@ -261,7 +261,7 @@
 
 	RW_CHECK_HEADER(fdt);
 
-	namep = (char *)fdt_get_name(fdt, nodeoffset, &oldlen);
+	namep = (char *)(uintptr_t)fdt_get_name(fdt, nodeoffset, &oldlen);
 	if (!namep)
 		return oldlen;
 
@@ -436,7 +436,7 @@
 	/* But if that overlaps with the old tree... */
 	if (((tmp + newsize) > fdtstart) && (tmp < fdtend)) {
 		/* Try right after the old tree instead */
-		tmp = (char *)fdtend;
+		tmp = (char *)(uintptr_t)fdtend;
 		if ((tmp + newsize) > ((char *)buf + bufsize))
 			return -FDT_ERR_NOSPACE;
 	}