zlib: import zlib files from zlib 1.2.11 ...

Import the following files from zlib 1.2.11:

   adler32.c
   crc32.c
   crc32.h
   inffast.c
   inffast.h
   inffixed.h
   inflate.c
   inflate.h
   inftrees.c
   inftrees.h
   zconf.h
   zlib.h
   zutil.c
   zutil.h

The original tarball is available from http://zlib.net/

The zlib is free software, distributed under the zlib license.  The
license text is included in the "zlib.h" file.  It should be compatible
with BSD-3-Clause.

The zlib license is included in the SPDX license list available at
https://spdx.org/licenses/, but I did not add the SPDX license tag to
the imported files above, to keep them as they are in the upstream
project.  This seems the general policy for ARM Trusted Firmware, as
SPDX License Identifier was not added to files imported from FreeBSD.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>