soc: renesas: rcar-sysc: Optimize rcar_sysc_area struct sizes

Reduce the sizes of the rcar_sysc_area and rcar_gen4_sysc_area
structures:
  - parent is in the range [-1..32] or [-1..64], so s8 is sufficient,
  - flags needs just 3 bits (for now), so u8 is plenty.

This reduces kernel size by:
  - 288 bytes for an R-Car Gen1+Gen2 kernel (arm32),
  - 1772 bytes for an R-Car Gen3+Gen4 kernel (arm64).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/cbbc8f464743d636895c048de61aa610d75392de.1654701156.git.geert+renesas@glider.be