md: Avoid namespace collision with bitmap API

commit e64e4018d572710c44f42c923d4ac059f0a23320 upstream.

bitmap API (include/linux/bitmap.h) has 'bitmap' prefix for its methods.

On the other hand MD bitmap API is special case.
Adding 'md' prefix to it to avoid name space collision.

No functional changes intended.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Shaohua Li <shli@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
[only take the bitmap_free change for stable - gregkh]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>