scsi: Use 'depends' with LIBFC instead of 'select'.

LIBFC depends upon SCSI_FC_ATTRS and select's CRC32C.

The only alternative would be to 'select' CRC32C and all of
SCSI_FC_ATTRS direct and indirect dependencies in the Kconfig section
for every LIBFCOE user which makes little sense.

Subsequently, use 'depends' instead of 'select' for LIBFCOE too.

Signed-off-by: David S. Miller <davem@davemloft.net>