MLK-15046-3 can: flexcan: make Message Buffer size and number dynamically

MLK-15046-3 can: flexcan: make Message Buffer size and number dynamically

The Message Buffer size and number will change in new Flexcan IP
version supporting CAN FD protocol. Let's make them properties and
assigned dynamically.

And note that when CAN FD is enabled, the FlexCAN RAM is partitioned
in blocks of 512 bytes, there may be hole within the block.
Thus a help macro FLEXCAN_CANFD_MB_OFFSET is introduced to calculate
the internal MB address offset properly within the RAM block.

Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>