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: I78ceee331cba2d691f68fd649bd5cf33f7868e72
Signed-off-by: Lakshmi Narayana Kalavala <lkalaval@codeaurora.org>