Use a map for GetDeviceUiKind

This makes it easier to add new device kinds, and reduces
the number of string comparisions when getting the device kind
Change-Id: Ife894fdb996adcccf73d2f9726c18a139590c132
Reviewed-on: https://weave-review.googlesource.com/1846
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
Reviewed-by: Vitaly Buka <vitalybuka@google.com>