GBE/libocl: Add __gen_ocl_get_timestamp() to get timestamp.

GBE/libocl: Add __gen_ocl_get_timestamp() to get timestamp.

Gen provide tm0 register for intra-kernel profiling.
Here we provide an API __gen_ocl_get_timestamp() to return
the timestamp in TM.

The return type is defined as:
struct time_stamp {
  ulong tick;
  uint event;
};

'tick' is a 64bit time tick. 'event' stores a value which means
whether a tmEvent has occured (non-zero) or not (0). tmEvent includes
time-impacting event such as context switch or frequency change
since last time tm0 was read.

I add a sample in the kernels/compiler_time_stamp.cl. Hope it
would help you understand how to use it.

V2:
Introduce ir::ARFRegister to avoid directly use of nr/subnr in Gen IR.
Rename __gen_ocl_extract_reg to __gen_ocl_region.
Rename beignet_get_time_stamp to __gen_ocl_get_timestamp.

Signed-off-by: Ruiling Song <ruiling.song@intel.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>