ARM: dts: msm: add external buck support

External buck presence will be detected based on the
HW ID and corresponding dt image will get selected and
the dt will override the latency values, spm commands
and enables the external buck support driver for sending
active set and sleep set votes to turn-on and turn-off
external buck by toggling a gpio.

CRs-fixed: 568380
Change-Id: I10c85291626bd7bb930e4ee386bc33e514b36e38
Signed-off-by: Anil kumar mamidala <amami@codeaurora.org>