ARM: dts: msm: change PM8998 LDO 20 default mode to HPM for SDM845

Change the default mode for PM8998 LDO 20 from LPM to HPM for
SDM845 boards.  This avoids a momentary droop of the UFS VCC
supply when software first requests a voltage (which sends the
device tree default low power mode as well) and then software
requests high power mode.

Change-Id: Iab58a2d5deb96026f48764435425e98f52166862
Signed-off-by: David Collins <collinsd@codeaurora.org>