can: kvaser_pciefd: Split driver into C-file and header-file.

Split driver into C-file and header-file, to simplify future patches.
Move common definitions and declarations to a header file.

Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Jimmy Assarsson <extja@kvaser.com>
Link: https://patch.msgid.link/20250725123230.8-7-extja@kvaser.com


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>