mke2fs: use lazy inode init on some discard-able devices

mke2fs: use lazy inode init on some discard-able devices

If a device supports discard -and- returns 0s for discarded blocks,
then we can skip the inode table initialization -and- the inode table
zeroing at mkfs time, and skip the lazy init as well since they are
already zeroed out.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>