msm: camera: add LED torch driver

User space should access the proper torch led sysfs node whose
driver is implemented according to led trigger frame work, so
camera need to provide such a node.

CRs-Fixed: 537513
Change-Id: I67458c16bf823824896051b93a6eb3067d5ae993
Signed-off-by: Xu Kai <kaixu@codeaurora.org>