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/libfdt_internal.h b/libfdt/libfdt_internal.h
index 2ba30db..549e345 100644
--- a/libfdt/libfdt_internal.h
+++ b/libfdt/libfdt_internal.h
@@ -77,19 +77,20 @@
 
 static inline void *_fdt_offset_ptr_w(void *fdt, int offset)
 {
-	return (void *)_fdt_offset_ptr(fdt, offset);
+	return (void *)(uintptr_t)_fdt_offset_ptr(fdt, offset);
 }
 
 static inline const struct fdt_reserve_entry *_fdt_mem_rsv(const void *fdt, int n)
 {
-	const struct fdt_reserve_entry *rsv_table = (struct fdt_reserve_entry *)
+	const struct fdt_reserve_entry *rsv_table =
+		(const struct fdt_reserve_entry *)
 		((const char *)fdt + fdt_off_mem_rsvmap(fdt));
 
 	return rsv_table + n;
 }
 static inline struct fdt_reserve_entry *_fdt_mem_rsv_w(void *fdt, int n)
 {
-	return (void *)_fdt_mem_rsv(fdt, n);
+	return (void *)(uintptr_t)_fdt_mem_rsv(fdt, n);
 }
 
 #define SW_MAGIC		(~FDT_MAGIC)