removal of #if NISADMA

[Reinoud Zandijk <reinoud%netbsd.org@localhost>]

> Would anyone have any objections to me splitting out the code from pmap.c
> that is surrounded by "#if NISADMA > 0" to it's own file ?
> 
> It would avoid the need for a dummy "device isadma" line in conf files
> for non ISA platforms.

Sure ! would be glad even ... the less clutter the better.... as
port-acorn32 portmaster i would say go !

Cheers,
Reinoud