expat: security bump to version 2.2.1

expat: security bump to version 2.2.1

Fixes:

- CVE-2017-9233 - External entity infinite loop DoS. See:
  https://libexpat.github.io/doc/cve-2017-9233/

- CVE-2016-9063 -- Detect integer overflow

And further more:

- Fix regression from fix to CVE-2016-0718 cutting off longer tag names.

- Extend fix for CVE-2016-5300 (use getrandom() if available).

- Extend fix for CVE-2012-0876 (Change hash algorithm to William Ahern's
  version of SipHash).

Also add an upstream patch to fix detection of getrandom().

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>