Revert "i965: Delete pre-DRI2.3 viewport hacks."

Revert "i965: Delete pre-DRI2.3 viewport hacks."

This reverts commit c9db037dc999eadbcaa8816c814e6ec1776d1a40.

Eric believes that the viewport hacks are still necessary for EGL;
invalidate events aren't hooked up properly.

This commit caused a regression where EFL applications wouldn't show
anything other than window decorations; GLBenchmark also showed issues.

The revert had conflicts due to the intel_context/brw_context merge.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=66606
Cc: mesa-stable@lists.freedesktop.org