HidHost: Use a non-zero value for enable event

HID host native uses 0 as both BTA_HH_ENABLE_EVT and empty event.
Any unplanned control channel message from the remote device can
generate and empty event. Such events cause the btif_hh to load the
bonded HID devices again.
This change creates a separate identifier for the empty event as 0. All
other event values are changed to accomodate this new event.

Bug: 330444923
Test: atest bluetooth_hh_test
Test: Manual | Pair and connect a HID device, disconnect and
reconnection using input device toggle in the device settings
Flag: EXEMPT minor bug fix

Change-Id: Icf770fc75a87d1a4612f2e06062d7b8b1f6a2010