Replace "unsigned long" by "u32" when handling 32-bit register data.

A.o., this saves 11 * 36 bytes in the static sh_eth_cpu_data structures
when compiling for 64-bit.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>