ARM: dts: msm: Add low latency level to device tree

Add low latency level to device tree. Values for low latency level is
regular and ultra. Regular stands for regular low latency and ultra
stands for ultra low latency. ULL is used on 8x10 and LL is used on
8974/8x26/8084.

Change-Id: I5f87a65ea35218ed1ff35b5fbab394d2574f0576
Signed-off-by: Krishnankutty Kolathappilly <kkolat@codeaurora.org>