msm: ipa3: enable smart prefetch control for GPI

Enable smart prefetch control for GPI channels.
This is done by configuring the channel scratch in GSI.

CRs-Fixed: 1000819
Change-Id: Iac1687b9b26eed715a1055cca295daa7b46f8abd
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>