pinctrl: renesas: Move R-Car bias helpers to sh_pfc.h

The Renesas Pin Function Controller driver uses two header files:
  - sh_pfc.h, for use by both core code and SoC-specific drivers,
  - core.h, for internal use by the core code only.

Hence move the R-Car bias helper declarations from core.h to sh_pfc.h,
and drop the inclusion of core.h from SoC-specific drivers that no
longer need it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20210303132619.3938128-3-geert+renesas@glider.be