Partially revert "st/xa: Fix advertized version number and try to avoid future discre...

Partially revert "st/xa: Fix advertized version number and try to avoid future discrepancies"

This reverts commit 61bedc3d6b08943f015f9d590c07a6af36c2a92c.

As the header is the one defining the API/ABI and is distributed
during installation, we should be using it rather than re-defining
the XA version in configure.ac.

Bump the version in the header to 2.2.0, to reflect what was the
original intent of commit 42158926c6d7d3ddbe61b9a04d60544ff1b50a96.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>