disp: msm: sde: remove vblank cache logic

Userspace is not supposed to request vblank until crtc is enabled,
because drm framework rejects the request if crtc is not enabled.
Any vblank request prior to that need to be cached in the userspace.
Hence removing the cache logic from the downstream driver.

Change-Id: I5383e39075377e3e49b8d335598ddfa48ab54666
Signed-off-by: Lakshmi Narayana Kalavala <lkalaval@codeaurora.org>