ARM: shmobile: R-Car: Shrink rcar_sysc_ch size

Shrink the individual fields in struct rcar_sysc_ch, as unsigned long or
int is overkill:
  - chan_offs contains a register offset relative to a base value
    (< 512),
  - chan_bit and isr_bit contain bit indices (0-31).

This reduces the size of each instance from 3 (4 on 64-bit) 32-bit words
to 1 32-bit word.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>