LU-12262 llite: harden ll_sbi ll_flags

LU-12262 llite: harden ll_sbi ll_flags

For most file systems mount flags are straight forward but this
is not the case for Lustre. We have to consider if the server
backend supports a mount option. Additionally its possible to
disable or enable a feature using sysfs during run time. Some
features can't be managed with a mount option but still can
be managed with sysfs or based on what is enabled on the server
node. All these states are reported together in the debugfs
file sbi_flags. The mount specific options are reported in
the super block show_option ll_show_option().

With all this complexity it is easy for it to get out of sync
and report incorrect things. We consolidate this handling by
moving to using match_table_t that is used by various Linux
file system to parse options. LL_SBI_FLAGS is replaced by our
match_table_t, ll_sbi_flags_name, that can be used for mount
options as well as reporting the sbi_flags in debugfs. We take
advantage of the fact that mount option parse will stop at the
first NULL in ll_sbi_flags_name and after that NULL list the
other features flags that are managed with other methods besides
mount options.

The next change is the move of ll_flags to a bitmap which gives
us two advantages. The first is that we can support more than
32 flags in the future. Second is no need to use bit shifting
math since we can use th enum LL_SBI_* values directly with
clear_bit() / set_bit() / test_bit(). Allow these changes should
miminize future problems with keeping all these states in sync.

Change-Id: Ia4f08cdde54c0fd11440dcf6b60b5fcb8bfb4d63
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/44541
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>