msm: mdss: remove process id based refcounting from fb

FrameBuffer driver is tracking each fb_open and fb_release
call with process id and file descriptor node. This is
duplicate logic to track single call. This change removes
process id based framebuffer driver call tracking to
reduce the complexity. File descriptor is different for
each call. That's the main reason for choosing it to
track the calls.

CRs-fixed: 716379
Change-Id: Ida1728d3878aeedf486bebef0f6f70c1e68d006e
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>