pinctrl: sh-pfc: sh73a0: Remove obsolete multi-platform check

pinctrl: sh-pfc: sh73a0: Remove obsolete multi-platform check

Since the removal of the sh73a0 legacy SoC code in commit
9a9863987bf7307f ("ARM: shmobile: Remove legacy SoC code for SH-Mobile
AG5"), sh73a0 is only supported in generic ARM multi-platform builds.
Hence CONFIG_ARCH_MULTIPLATFORM is always set, and the check can be
removed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>