Add kernels performance output

Add kernels performance output

if environment variable OCL_OUTPUT_KERNEL_PERF is set non-zero,
then after the executable program exits, beignet will output the
time information of each kernel executed.

v2:fixed the patch's trailing whitespace problem.

v3:if OCL_OUTPUT_KERNEL_PERF is 1, then the output will only
contains time summary, if it is 2, then the output will contain
time summary and detail. Add output 'Ave' and 'Dev', 'Ave' is
the average time per kernel per execution round, 'Dev' is the
result of 'Ave' divide a kernel's all executions' standard deviation.

Signed-off-by: Yongjia Zhang <yongjia.zhang@intel.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>