wwan: core: Use the bitmap API to allocate bitmaps

wwan: core: Use the bitmap API to allocate bitmaps

Use bitmap_zalloc() and bitmap_free() instead of hand-writing them.
It is less verbose and it improves the type checking and semantic.

While at it, add missing header inclusion (should be bitops.h,
but with the above change it becomes bitmap.h).

Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230911131618.4159437-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>