ARM: shmobile: Move SoC Kconfig symbols to drivers/soc/renesas/

For consistency with arm64, where vendors have a single Kconfig symbol
in arch/arm64/Kconfig.platforms.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>