feat(zlib): update zlib source files

Upgrade the zlib source files to the ones present in the version 1.2.13
of zlib [1]. Since 1.2.11 the use of Arm crc32 instructions has been
introduced so update the files to make use of this.

[1] https://github.com/madler/zlib/tree/v1.2.13

Change-Id: Ideef78c56f05ae7daec390d00dcaa8f66b18729e
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/Makefile b/Makefile
index 8adc0d0..2c3f23d 100644
--- a/Makefile
+++ b/Makefile
@@ -59,6 +59,7 @@
 					lib/compiler-rt			\
 					lib/libfdt%			\
 					lib/libc,			\
+					lib/zlib			\
 					$(wildcard lib/*)))
 ROOT_DIRS_TO_CHECK	:=	$(sort $(filter-out			\
 					lib				\