mesa: Enable remap table in core.

mesa: Enable remap table in core.

This enables the remap table in core.  driInitExtensions is adapted to
use the remap table.  All uses of extension_helper.h are replaced by
remap_helper.h.  The chicken-egg problem of the DRI drivers is also
solved.

It is now also possible to pass NULL extensions to driInitExtensions.
It will cause driInitExtensions to map all known functions.  This
functionality is used by software drivers and EGL_i915.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>