libffi: upgrade 3.4.6 -> 3.4.7

libffi: upgrade 3.4.6 -> 3.4.7

Changelog:
==========
- Add static trampoline support for Linux on s390x.
- Fix BTI support for ARM64.
- Support pointer authentication for ARM64.
- Fix ASAN compatibility.
- Fix x86-64 calls with 6 GP registers and some SSE registers.
- Miscellaneous fixes for ARC and Darwin ARM64.
- Fix OpenRISC or1k and Solaris 10 builds.
- Remove nios2 port.

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>