isa arch-dependent and arch-independent

[Yonghong Yan]

the codes for isa bus in pc32/i386: the arch-independent is in
sys/bus/isa, and a folder under that, i.e. i386, is for i396-specific.
But also found another folder in sys/platform/pc32/isa that is
arch-dependent. should the sys/bus/isa/i386/* be merged to
sys/platform/pc32/isa/?

also, the sys/bus/isa/pnpeat.c (an i386-dependent file in the
arch-independent folder) seems not used anywhere, remove it?

Thanks
Yonghong