msm: qmi: Add support to encode and send zero length QMI messages

Currently when the clients try to send zero length QMI requests, QMI
encode/decode library returns an invalid error code.

Update the encode/decode library to check if a minimum message length
of a QMI message can be zero and enable sending such zero length QMI
messages.

Change-Id: Ifa0241107b67cc316d7ef4ba8e45bca21feb87da
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>