msm: vidc: Register CVP node conditionally

Conditional check is put to check if CVP node exists.
Added a new API to remove redundant part in code.
Unregistered CVP node in case of the cores_exceeded error.

Change-Id: Ife58a748b71a35398b8eeac6782c8d4ad616f31d
Signed-off-by: Shubham Gupta <shubgupt@codeaurora.org>