qcaux: add driver for QCDM-capable ports on various devices

Many Qualcomm-based devices provide a CDC-ACM port which accepts
normal AT commands and PPP connections.  But they only provide one
which makes status or signal strength requests impossible while
PPP is active.  They also provide secondary USB interfaces that
talk the Qualcomm Diagnostic Monitor (QCDM) protocol which can be
used for status and strength.  Make those QCDM ports accessible.
Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>