snd_hdsp(4): RME HDSP 9632 and HDSP 9652 sound card driver.

Add a sound(4) bridge device driver for the RME HDSP 9632 and HDSP 9652
sound cards. These cards require a nowadays rare PCI 32bit (not PCIe)
slot, but still see use due to their value and wealth of features.
The HDSP 9632 is mostly comparable to the newer HDSPe AIO, while the
HDSP 9652 is similar to the HDSPe RayDAT. These HDSPe PCIe cards are
supported by the snd_hdspe(4) driver which was taken as a starting point
for development of snd_hdsp(4).

Implementation is kept separately due to substantial differences in
hardware configuration and to allow easy removal in case PCI 32bit
support would be phased out in the future.

The snd_hdsp(4) kernel module is not enabled by default, and can be
loaded at runtime with kldload(8) or during boot via loader.conf(5).
Basic operation was tested with both cards, not including all optional
cable connectors and expansion boards. Features should be roughly on par
with the snd_hdspe(4) supported cards.

Reviewed by: christos, br
Differential Revision: https://reviews.freebsd.org/D45112