staging: comedi: ni_mio_common: tidy up mite dma channel requests

staging: comedi: ni_mio_common: tidy up mite dma channel requests

Tidy up the functions that request the mite dma channels by absorbing the
inline helper functions that call ni_set_bitfield() to set the channel
selection bits.

Add support for the NI_M_CDIO_DMA_SEL_REG register to ni_set_bitfield()
so that all the soft_reg_copy_lock spinlocking is done in one place.

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