LU-16697 llite: Set BDI_CAP_* flags for lustre

LU-16697 llite: Set BDI_CAP_* flags for lustre

Lustre should set the BDI_CAP_* flags and the s_iflags
to indicate support for write back and cgroup write back

HPE-bug-id: LUS-11553
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: I49ce07fce8a9d153b9a71d8a0ba28b799354fc7f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50497
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>