Add va_MessagingInit().

Add va_MessagingInit().

Previous to this commit, changing verbosity level
was only possible at build time via the definition
of ENABLE_VA_MESSAGING.

Now it's possible to choose a verbosity level between
{0, 1, 2} by modifying /etc/libva.conf or by setting
the corresponding environment variable LIBVA_MESSAGING_LEVEL.

Signed-off-by: Giuseppe <giuscri@gmail.com>
(cherry picked from commit b4d0874dcbe99d1f47bd39d0c156ea89ecd0ebcc)