opencl: use versioned .so in mesa.icd

We must have versioned library in mesa.icd, because ICD loader would
fail if the mesa-devel package wasn't installed.

Reported-by: Fabian Deutsch <fabian.deutsch@gmx.de>
Reference: https://bugs.freedesktop.org/show_bug.cgi?id=73512
Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>