btrfs: export bitmap_test_range_all_{set,zero}

bitmap_test_range_all_{set,zero} defined in subpage.c are useful for other
components. Move them to misc.h and use them in zoned.c. Also, as
find_next{,_zero}_bit take/return "unsigned long" instead of "unsigned
int", convert the type to "unsigned long".

While at it, also rewrite the "if (...) return true; else return false;"
pattern and add const to the input bitmap.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>