sh: Kill off obsolete busses from arch/sh/Kconfig.

ISA can go away now that the hd6446x PCMCIA drivers no longer exist
in-tree. The rationale for enabling CONFIG_ISA in the first place is
likewise no longer valid given that the subsystem has changed since
the time that assertion was valid.

While we are at it, kill off SBUS, MCA, EISA, and so on. These are
not supported and never will be.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>