staging: comedi: c6xdigio: consolidate the board_init()

For aesthetics, rename this function so it has namespace associated
with the driver.

Absorb the c6xdigio_pwm_init() and c6xdigio_encoder_reset() helpers.

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>