fix alpha ISA support

isa_bus_to_virt() is still needed in a few places (lance.c, at least).  When
we switch the kernel to using -Werror-implicit-function-declaration, the lack
of isa_bus_to_virt() breaks alpha allmodconfig builds.

Add isa_bus_to_virt() and deprecate the ezisting ISA APIs, though it might be
better to define these functions as BUG(), since virt_to_bus/bus_to_virt just
do wrong things on a number of machines.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>