ARM: dts: msm: Modify IPA poll parameters for MSM8920

Throughput KPI's are impacted with the current poll parameters.
Make a change to use 2ms poll sleep and 5 empty poll iterations
which satisfies both power and performance kpi's.

Change-Id: I7f74a33d165c3ba0999b75bd1f21e03870c852e5
Acked-by: Chaitanya Pratapa <cpratapa@qti.qualcomm.com>
Signed-off-by: Utkarsh Saxena <usaxena@codeaurora.org>