msm: mdss: Fix race conditions during device shutdown

Wait for the display commit thread to exit and abort all
pending ioctls when releasing the framebuffer device. This is
necessary to address any potential race conditions between these
threads that operate on a common data structure.

Change-Id: I5ab32758c34d4e80c4e85f949ffa0054d3cb5340
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>