arm64: defconfig: add support for Socionext SynQuacer based platforms

Enable support in arm64's defconfig for Socionext SynQuacer based
platforms, by enabling the arch Kconfig symbol, and enabling builtin
support for the ethernet, GPIO and SDHCI controllers

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>