Bump library major version.

Bump library major version.

The whole libgstvaapi libraries got a major refresh to get rid of GObject.
This is a fundamental change that requires a new SONAME. More changes are
underway to streamline the core libraries.

So far, the net result is a reduction of .text size (code) by 32KB, i.e. -10%.
On one particular test (sintel HD trailer), the total number of executed
instruction was reduced by 8%.