dm: add emulated block size target

This new target is similar to the linear target except that it emulates
a smaller logical block size on a device with a larger logical block
size.  Its main purpose is to emulate 512 byte sectors on 4K native
disks (i.e. 512e).

See Documentation/admin-guide/device-mapper/dm-ebs.rst for details.

Reviewed-by: Damien Le Moal <DamienLeMoal@wdc.com>
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org> [Kconfig fixes]
Signed-off-by: Zheng Bin <zhengbin13@huawei.com> [static fixes]
Signed-off-by: Mike Snitzer <snitzer@redhat.com>