libqmi: add optional features

libqmi: add optional features

The libqmi library and tools come with several optional features that
may be enabled or disabled during build.

This patch adds support to automatically enable or disable them based
on the presence of the required dependencies for each:
 * QMI-over-MBIM is enabled if libmbim is selected.
 * udev support in qmi-firmware-update is enabled if libgudev is
   selected.
 * MM runtime check in qmi-firmware-update is enabled if ModemManager
   is selected (but we don't build-depend on it, the runtime check is
   done using plain glib2 DBus operations).

Signed-off-by: Aleksander Morgado <aleksander@aleksander.es>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>