libffi: bump to 3.1

libffi: bump to 3.1

Status of the patches:

 - libffi-001-Fix-installation-location-of-libffi.patch, preserved.
 - libffi-002-Fix-use-of-compact-eh-frames-on-MIPS.patch, preserved
 - libffi-arc-01-Add-ARC-support.patch, removed, ARC support was
   merged upstream as of commit b082e15091961373c03d10ed0251f619ebb6ed76.
 - libffi-arc-02-Rebuild-for-ARC-additions.patch, removed, this patch
   was merged upstream as of commit
   0f8690a84c874ec09a090c8c6adfb93c594acac6.
 - libffi-003-fix-typo.patch, added, reported on the upstream mailing
   list as being necessary, will be part of the next 3.1.1 release.
 - libffi-004-Add-missing-GNU-stack-markings-in-win32.S.patch, same
   status as patch 003.
 - libffi-005-Fix-paths-in-libffi.pc.in.patch, same status as patch
   003.

The 3.1 release adds support for a number of architectures: ARC
support, ppc64le support, NIOS II support. See
https://sourceware.org/ml/libffi-announce/2014/msg00000.html for
details.

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