relational: Implement shuffle builtin

This was added in CL 1.1

Tested with a Radeon HD 7850 (Pitcairn) using the CL CTS via:
test_conformance/relationals/test_relationals shuffle_built_in

v2: Add half-precision support to shuffle when available.
    Move to misc/ and add section 6.12.12 to clc.h

Signed-off-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Jan Vesely <jan.vesely@rutgers.edu>
llvm-svn: 312403