media: Convert IsPMIEnabled to static

This CL converts the function 'IsProtectedMediaIdentifierEnabled'
to static, so that we can call it in places without instantiating
an object.

Bug: b/274654543
Change-Id: I79ad3376cd57ca46f3e2f16c32edffebe921e83a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4575178


Reviewed-by: John Rummell <jrummell@chromium.org>
Commit-Queue: Vikram Pasupathy <vpasupathy@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1151381}