msm: camera: support simple led flash controlled by one gpio for SKUAB

SKUAB uses a low cost led for camera flash, the led is driven by
system power, and use a transistor controlled by external pin to
gate its on/off state. This is also a single mode flash led with
no difference between flash mode and torch mode. So we need to add
support for this in camera driver.

CRs-fixed: 561538
Change-Id: Ia0c9f6a33e404457c018a719d68fe5f7a6f22029
Signed-off-by: Xu Kai <kaixu@codeaurora.org>