Add "uinput" command to support uinput device.

Add support of uinput device with "uinput" shell command, allows user to
create a virtual uinput device and inject events to it, for input
framework testing.

Bug: 160360195
Bug: 163217897

Test: run uinput command from adb shell.
Change-Id: Ic885ae510d98fa282722f7a17d66778c15a893b6