x86: add linux kernel support for YMM state

Impact: save/restore Intel-AVX state properly between tasks

Intel Advanced Vector Extensions (AVX) introduce 256-bit vector processing
capability. More about AVX at http://software.intel.com/sites/avx

Add OS support for YMM state management using xsave/xrstor infrastructure
to support AVX.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1239402084.27006.8057.camel@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>