CVE-2023-52586 drm/msm/dpu: Add mutex lock in control vblank irq

In the Linux kernel, the following vulnerability has been resolved:

drm/msm/dpu: Add mutex lock in control vblank irq

Add a mutex lock to control vblank irq to synchronize vblank
enable/disable operations happening from different threads to prevent
race conditions while registering/unregistering the vblank irq callback.

v4: -Removed vblank_ctl_lock from dpu_encoder_virt, so it is only a
parameter of dpu_encoder_phys.
-Switch from atomic refcnt to a simple int counter as mutex has
now been added
v3: Mistakenly did not change wording in last version. It is done now.
v2: Slightly changed wording of commit message

Patchwork: https://patchwork.freedesktop.org/patch/571854/