Adding feature: input device disable/enable

This functionality will only be available for signed system
services. 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: CTS test - android.view.cts.InputDeviceEnabledTest
Native test - WhenEnabledChanges_SendsDeviceResetNotification,
WhenDeviceCreated_EnabledIsTrue. Also developed a custom apk
with signature permission that calls disable/enable on a
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.

Change-Id: I99a7866cebff873dc1848e11a39045ed2eaec07c