drm: msm: add uevent handler to release pipes

To achieve glitch-free purpose for early RVC case, the pipes are set
to be unavailable to user Apps. So after splash handoff is done, kernel
needs to tell user Apps the update via this uevent. User Apps will get
this event and start further operation accordingly.

CRs-Fixed: 2225630
Change-Id: I96f023d72dea9c359730d0313e65e87cf9dc1fbc
Signed-off-by: Guchun Chen <guchunc@codeaurora.org>