dm integrity: add the "reset_recalculate" feature flag

Add a new flag "reset_recalculate" that will restart recalculating
from the beginning of the device. It can be used if we want to change
the hash function. Example:

dmsetup remove_all
rmmod brd
set -e
modprobe brd rd_size=1048576
dmsetup create in --table '0 2000000 integrity /dev/ram0 0 16 J 2 internal_hash:sha256 recalculate'
sleep 10
dmsetup status
dmsetup remove in
dmsetup create in --table '0 2000000 integrity /dev/ram0 0 16 J 2 internal_hash:sha3-256 reset_recalculate'

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>