be2net: Use Kconfig flag to support for enabling/disabling adapters

Add flags to enable/disable supported chips in be2net.

With disable support are removed coresponding PCI IDs and
also codepaths with [BE2|BE3|BEx|lancer|skyhawk]_chip checks.

Disable chip will reduce module size by:
BE2 ~2kb
BE3 ~3kb
Lancer ~10kb
Skyhawk ~9kb

When enable skyhawk only it will reduce module size by ~20kb

New help style in Kconfig

Reviewed-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: Petr Oros <poros@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>