disp: msm: sde: update TEAR_SYNC_WRCOUNT register before vsync counter

During DMS, when tear check registers are updated near
rd_ptr line count, it was resulting in a spurious
rd_ptr_irq to which frame is getting latched and causing
tearing on the screen. This change updates
TEAR_SYNC_WRCOUNT register before disabling the vsync
counter and adds a spinlock to avoid pre-emption.

Change-Id: I986dc3ce6fb3da5fed758c2f50562df44f2ab557
Signed-off-by: Yashwanth <quic_yvulapu@quicinc.com>