pinctrl: renesas: Move drive strength configuration into sh_pfc_soc_operations

pinctrl: renesas: Move drive strength configuration into sh_pfc_soc_operations

The upcoming Renesas R-Car Gen5 uses different mapping of bits in DRV
control register, which is incompatible with existing DRV register bit
mapping. Add .set_drive_strength callback into sh_pfc_soc_operations
and call it from sh_pfc_pinconf_set(), to allow each SoC specific PFC
driver to implement replacement .set_drive_strength. Make the current
sh_pfc_pinconf_set_drive_strength() non-static, rename it with rcar_
prefix, and pass it as .set_drive_strength for existing PFC drivers.
This is a preparatory patch for R-Car Gen5, no functional change.

Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
[Marek: Consistently use .set_drive_strength() and pass exisiting
        sh_pfc_pinconf_set_drive_strength() as its parameter for
	all PFC drivers. Rewrite commit message.]