lib/hexdump: Use `size_t` for length parameter of `hexdump32()`

In the signature of the function `hexdump32()` it does not make sense to
represent a length, assumed to be positive, as a signed integer.
With this change, it is no longer necessary to cast a pointer to
unsigned long when passing it to `hexdump32()`.

The same change for the function `hexdump()` was done in commit
3dd0e72d [1].

	lib/hexdump: Take const void * and size_t as arguments

[1] http://review.coreboot.org/4575

Change-Id: Id97f5daff95f94e862ee8b5be896a6629b125a13
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/5646
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/include/lib.h

@@ -52,6 +52,6 @@ extern unsigned char _estack[];
 
 /* Defined in src/lib/hexdump.c */
 void hexdump(const void *memory, size_t length);
-void hexdump32(char LEVEL, const void *d, int len);
+void hexdump32(char LEVEL, const void *d, size_t len);
 
 #endif /* __LIB_H__ */

src/lib/hexdump.c

@@ -62,7 +62,7 @@ void hexdump(const void *memory, size_t length)
 	}
 }
 
-void hexdump32(char LEVEL, const void *d, int len)
+void hexdump32(char LEVEL, const void *d, size_t len)
 {
 	int count = 0;