Split fastpath array to two, i.e. for mask and for bits.
At the same time declare them as bitmaps.

This makes code better to read and gives a clue about use of
bitmap API.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>