Adding feature: input device disable/enable.

This functionality will only be available for signed system applications.
A disable call will cause a file descriptor to the input device
driver to be closed, which in turn may cause the input device
to switch into a low-power mode.
An enable call will reopen the input device.

Bug: 30143923
Test: developed a custom apk with signature permission that
calls disable/enable on touchscreen device. Verified that
touchscreen stops working when disable is called and starts
working again when enable is called. Verified that the file
handle to the driver is closed and reopened. Verified that
the notification onInputDeviceChanged is received in the app.
CTS test - android.view.cts.InputDeviceEnabledTest

Change-Id: I1e42c6996e679c083cd3f0c9adfaef8ba22c4ee4