msm: mdss: Replace vsync work queue with sysfs_notify_dirent

Since sysfs_notify_dirent() can be called in interrupt context,
use it instead of work queue. This should improve latency of
vsync events, especially as work queues run at normal
priority, and the other threads which transmit vsync events use
a higher priority.

Change-Id: I14de54b455ed5cc17b61e1e9ff9078b8c958cdcb
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>