msm: gsi: Add support for EV RP DDR access feature

Allocate memory on DDR for event RP and providing it
to the GSI context.
Accessing the event RP using the DDR pointer instead
of reading the GSI register.

Change-Id: Ib25ae4ee8abbc73a74f24d360f64b1295a9d4520
Acked-by: Nadav Levintov <nadavl@qti.qualcomm.com>
Signed-off-by: Sivan Reinstein <sivanr@codeaurora.org>