staging: comedi: rtd520: convert driver to attach_pci

Convert this driver to use the comedi PCI auto config mechanism
by adding an attach_pci callback.

Since this driver requires no extra configuration options, and
the attach callback is now optional, remove it.

Use the found 'dev->board_name' for the resource name passed to
comedi_pci_enable() and request_irq().

Since this driver no longer walks the pci bus to find the pci_dev,
remove the pci_dev_put() in the detach.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>