[PATCH] ISA DMA Kconfig fixes - part 1

A bunch of drivers use ISA DMA helpers or their equivalents for
platforms that have ISA with different DMA controller (a lot of ARM
boxen).  Currently there is no way to put such dependency in Kconfig -
CONFIG_ISA is not it (e.g.  it is not set on platforms that have no ISA
slots, but have on-board devices that pretend to be ISA ones).

New symbol added - ISA_DMA_API.  Set when we have functional
enable_dma()/set_dma_mode()/etc.  set of helpers.  Next patches in the
series will add missing dependencies for drivers that need them.

I'm very carefully staying the hell out of the recurring flamefest on
what exactly CONFIG_ISA would mean in ideal world - added symbol has a
well-defined meaning and for now I really want to treat it as completely
independent from the mess around CONFIG_ISA.

Signed-off-by: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>