bfin_can: Merge header file from arch dependent location

Header file was in arch dependent location arch/blackfin/include/asm/bfin_can.h,
Now move and merge the useful contents of header file into driver code, note
the original header file is reserved for full registers set access test by other
code so it survives.

Signed-off-by: Aaron Wu <Aaron.wu@analog.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>