i965: Require Kernel 3.6 for Gen4-5 platforms.

i965: Require Kernel 3.6 for Gen4-5 platforms.

We've already required Kernel 3.6 on Gen6+ since Mesa 9.2 (May 2013,
commit 92d2f5acfadea672417b6785710c9e8b7f605e41).  It seems reasonable
to require it for Gen4-5 as well, bumping the requirement from 2.6.39.

This is necessary for glClientWaitSync with a timeout to work, which
is a feature we expose on Gen4-5.  Without it, we would fall back to an
infinite wait, which is pretty bad.

See kernel commit 172cf15d18889313bf2c3bfb81fcea08369274ef in 3.6+.

Reviewed-by: Matt Turner <mattst88@gmail.com>