md: add the bitmap group to the default groups for the md kobject

mainline inclusion
from mainline-v5.16-rc1
commit 51238e7f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I81XCK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=51238e7fbd6182e36dbc093c92ae93142c57c0f5



--------------------------------

Replace the deprecated default_attrs with the default_groups mechanism,
and add the always visible bitmap group to the groups created add
kobject_add time.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Li Nan <linan122@huawei.com>