bitmap: add test for bitmap_*_region() functions

Test basic functionality of bitmap_{allocate,release,find_free}_region()
functions.

CC: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>