mesa: Add SSE 4.1 optimisation for glDrawElements.

mesa: Add SSE 4.1 optimisation for glDrawElements.

Makes use of SSE 4.1 to speed up compute of min and max elements.

Callgrind cpu usage results from pts benchmarks:

Openarena 0.8.8: 3.67% -> 1.03%
UrbanTerror: 2.36% -> 0.81%

V5:
- actually make use of the optimisation in android (Emil Velikov)
- set a better array size limit for using SSE and added TODO

V4:
- fixed bugs with incrementing pointer and updating counters

V3:
- Removed sse_minmax.c from Makefile.sources
- handle the first few values without SSE until the pointer is aligned
 and use _mm_load_si128 rather than _mm_loadu_si128
- guard the call to the SSE code better at build time

V2:
- removed GL* types
- use _mm_store_si128() rather than _mm_store_ps()
- add runtime check for SSE
- use aligned attribute for local mix/max
- bunch of tidyups

Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Timothy Arceri <t_arceri@yahoo.com.au>