s390/lcs: Remove FDDI option

s390/lcs: Remove FDDI option

The last s390 machine that supported FDDI was z900 ('7th generation',
released in 2000). The oldest machine generation currently supported by
the Linux kernel is MARCH_Z10 (released 2008). If there is still a usecase
for connecting a Linux on s390 instance to a LAN Channel Station (LCS), it
can only do so via Ethernet.

Randy Dunlap[1] found that LCS over FDDI has never worked, when FDDI
was compiled as module. Instead of fixing that, remove the FDDI option
from the lcs driver.

While at it, make the CONFIG_LCS description a bit more helpful.

References:
[1] https://lore.kernel.org/netdev/20230621213742.8245-1-rdunlap@infradead.org/

Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230724131546.3597001-1-wintera@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>