mkimage : Split out and clean pbl_crc32 for use by other image types

The crc32 used by pblimgae is NOT the same as zlib crc32.

The pbl_crc32 is useful for other purposes in mkimage so split it out.

While we are about it, clean up redundant and confusing code.

Signed-off-by: Charles Manning <cdhmanning@gmail.com>
diff --git a/tools/Makefile b/tools/Makefile
index 7610557..cbf00d5 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -91,6 +91,7 @@
 			omapimage.o \
 			os_support.o \
 			pblimage.o \
+			pbl_crc32.o \
 			sha1.o \
 			sha256.o \
 			ublimage.o \