ARM: dts: msm: add PMI8998 PMIC peripheral devices

Add a new device tree file pmi8998.dtsi which contains devices
for the PMIC peripherals found in PMI8998 chips.

This file is based upon msm-pmi8998.dtsi found in the msm-4.4
branch as of:

commit b8c4038d1470 ("Merge "msm: mdss: Handling possible
integer overflow"").

Change-Id: I96604b46bd5d6b18078de76bb4419eda9b132aa0
Signed-off-by: David Collins <collinsd@codeaurora.org>