msm: vidc: Replace macro to find kernel message tag with static function

Macro VIDC_MSG_PRIO2STRING returns message tag for the given debug level.
Replacing this macro with a static function to comply with kernel
guideline.

CRs-Fixed: 2178329
Change-Id: If44b7bef463fa00c37534cda9a86f00bcba4904a
Signed-off-by: Karthikeyan Periasamy <kperiasa@codeaurora.org>