pinctrl: renesas: Remove sh_pfc_config_mux_for_gpio()

pinctrl: renesas: Remove sh_pfc_config_mux_for_gpio()

This function is now replaced by common pin controller GPIO configuration
functionality, drop it.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Alex Kiernan <alex.kiernan@gmail.com>
Cc: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Cc: Eugeniu Rosca <roscaeugeniu@gmail.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Patrick DELAUNAY <patrick.delaunay@st.com>
Cc: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Cc: Simon Glass <sjg@chromium.org>