msm: gsi: construct TRE before submit

For performance improvement avoid multiple writes to channel ring
which is a dma coherent memory. Instead, construct the TRE
(Transfer Ring Element) in local memory and then copy it to the
ring itself.

Change-Id: I36bfae306be2a90c8679d416397a435e638b54eb
CRs-Fixed: 977590
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>