msm: vidc: Ignore thumbnail session load

Thumbnail sessions are considered to be non realtime
sessions. Hence ignore the thumbnail sessions load on
device while calculating the load and mark thumbnail
sessions as perf session.

Change-Id: Ifa89c2f670fa631b6805a5d796a04e07e294ca4c
Signed-off-by: Priyanka Gujjula <pgujjula@codeaurora.org>