new system is integrated with the ISA bus code more cleanly and allows
the future addition of more enumerators such as PnPBIOS and ACPI.
This commit also enables the new pcm driver since it is somewhat tied to
the new PnP code.
* Re-work the resource allocation code to use helper functions in subr_bus.c.
* Add simple isa interface for manipulating the resource ranges which can be
allocated and remove the code from isa_write_ivar() which was previously
used for this purpose.