Revert "configure: Disable xvmc by default"

Revert "configure: Disable xvmc by default"

This reverts commit 6a19bb56e09e841553ad1295f74fa21bfbbe752a.

The above commit disabled the default build of xvmc as the xvmc tests
were failing. As pointed out by Ilia, the tests are "broken by design"
as they do not test the object that is build but the one that is
installed and setup on the workstation.

With previous commit we moved the programs from the 'make check' to
noinst automake target. This way they won't be run but will be around
for people to use them.

Cc: Tom Stellard <thomas.stellard@amd.com>