test_bits: add tests for BIT_U*()

Add some additional tests in lib/tests/test_bits.c to cover the
expected results of the fixed type BIT_U*() macros.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>