x86: Add support for the clflushopt instruction

x86: Add support for the clflushopt instruction

Add support for the new clflushopt instruction.  This instruction was
announced in the document "Intel Architecture Instruction Set Extensions
Programming Reference" with Ref # 319433-018.

http://download-software.intel.com/sites/default/files/managed/50/1a/319433-018.pdf

[ hpa: changed the feature flag to simply X86_FEATURE_CLFLUSHOPT - if
  that is what we want to report in /proc/cpuinfo anyway... ]

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Link: http://lkml.kernel.org/r/1393441612-19729-2-git-send-email-ross.zwisler@linux.intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>