The commit adds kernel.h header at the top level of xtos-wrapper
include directory. The idea is to be able to write OS agnostic code
using Zephyr kernel API calls and simply including kernel.h without
worrying if we are building for XTOS or Zephyr.
This first commit contains Zephyr API style k_msleep() and k_usleep()
implementations. The functions in fact call the old
wait_delay-functions.
More implementations and declarations following Zephyr kernel.h
content can be added as needed.
Signed-off-by: Jyri Sarha <jyri.sarha@intel.com>