drivers: can: mcan: refactor to get rid of wrapper functions

Refactor the Bosch M_CAN shared driver functions to get rid of the
front-end driver wrapper functions.

This requires flipping the relationship between shared config/data
structs and front-end config/data structs. Front-end drivers can now
store a pointer to their custom config/data structs in the .custom
fields of the can_mcan_config and can_mcan_data data structures.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>