ext4: add discard/zeroout flags to journal flush

Add a flags argument to jbd2_journal_flush to enable discarding or
zero-filling the journal blocks while flushing the journal.

Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Link: https://lore.kernel.org/r/20210518151327.130198-1-leah.rumancik@gmail.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>