libinput: add configure arg and PACKAGECONFIG for libunwind

libinput: add configure arg and PACKAGECONFIG for libunwind

libinput uses pkg-config to check and decide whether to build
with libunwind, which causes undeterministic builds or error:

| tmp/work/core2-64-wrs-linux/libinput/0.18.0-r0/libinput-0.18.0/test/litest.c:77:23:
| fatal error: libunwind.h: No such file or directory

So add configure arg and PACKAGECONFIG for libunwind to make
deterministic build, but libunwind is disabled by default.

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>