crimson/osd: use a unified super-block for devices

crimson/osd: use a unified super-block for devices

This commit refactors the on-hardware super-block structure
used by the seastore to a unified format that
can accommodate all three device types (HDD, ZBD, RBM).

All devices now have a 60 bytes header at address 0,
similar to the existing BlueStore layout. A 23-byte magic
string ("CRIMSON_DEVICE") is placed at the beginning of
the header, followed by 37 bytes of null padding (to
match the existing 60 bytes of the super-block), and
then the DENC-encoded device_superblock_t structure starting
at offset 60.

A unified device_config_t is now used for all device types.

The per-shard data structure is also unified, now including a union
of all relevant fields for each device type.

We are also adding a check for the super-block magic value in the
RBMDevice::read_rbm_superblock() method, similar to the existing check
in SegmentManager::read_segment_manager_superblock().

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>