Link libinput as static_lib for libinput_tests

When doing test-driven development, it's often needed to update the
libinput library when iterating on the CL.

Link libinput statically to allow for simpler invocation of the tests.
Now, 'atest' will use the latest version of libinput when running
libinput_tests, without having to do "adb sync".

Bug: 167946721
Test: atest libinput_tests
Change-Id: I9f6335f163d197d82f7654c7ad3cda0d19ff3852