The first round of I/O space pointers separation.

The new 2.6.x Linux kernels separates I/O space
addresses from kernel and user space ones.
They are defined as (void __iomem *).
To follow this rule and suppress some warnings
LinCAN defines type can_ioptr_t now which allows
to keep code compatible between 2.4.x and 2.6.x kernels.
These changes exposes more other inconsistencies
in some boards support code which should be corrected
one by one later.

The code requires testing and checking on more hardware.