pinctrl: renesas: Reintroduce SH_PFC for common sh-pfc code

pinctrl: renesas: Reintroduce SH_PFC for common sh-pfc code

Most, but not all, Renesas pin control drivers use the "sh-pfc" pin
control framework.  As of commit 8449bfa9e6a9f7ec ("pinctrl: sh-pfc:
Collect Renesas related CONFIGs in one place"), the code for this
framework is always built when Renesas SoC pin control support is
enabled, regardless of whether the enabled pin control drivers need it
or not.

Fix this by reintroducing the CONFIG_SH_PFC symbol to control inclusion
of the "sh-pfc" framework and its dependencies, and selecting it when
needed.

This reduces kernel size of a typical RZ/A1 or RZ/A2 kernel by more than
6 resp. 11 KiB.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200909131534.12897-4-geert+renesas@glider.be