msm: ipa: send the endp_desc QMI for low_lat only on non-auto mode

There is no low_lat use case on auto mode, so the ep mapping is
not defined.
Add sanity check to not sent endp_desc QMI for ep which is not
defined.
Add check to make sure send endp_desc specific to low lat only
for mhi non-auto case.

Change-Id: I6fe72556433c0ac84772411cc5b1ac99bcadc30e
Signed-off-by: Bojun Pan <bojunp@codeaurora.org>