ext2fs: Add large sectorsize disks support

The ext2fs does not support disks with sectorsize more 512 bytes.
The main issue is in reading/writing superblock, which is not aligned
with 4k value. Reimplement the superblock reading logic to make it
indifferent to disk logical sector size. The logical sector size
more then page size is not supported, like it is doing on Linux side.

PR: 271105
Reported by: k(at)vodka.home.kg
Reviewed by: pfg
MFC after: 2 week
Differential Revision: https://reviews.freebsd.org/D40047