[Mesa-dev] Janitorial work: no more intel_context.[ch]; tidying

[Kenneth Graunke]

This series combines brw_context.[ch] and intel_context.[ch],
and cleans up our context creation code quite a bit.  A bunch of
functionality was awkwardly split between the two sets of files;
now it's all in one place.

While this series is large, it should be fairly easy reading.
Patch 28 does have one functional change on 32-bit systems - it removes
a handcoded assembly version of memcpy.  This has not been tested.

Available as 'tidying6' in my tree.  Based on Eric's megadriver-prep series.