Provide the ARCH_MESON Kconfig symbol for the Amlogic S905 SoCs.

* tag 'for-v4.6/gxbb-arm64' of https://github.com/carlocaione/linux-meson:
  ARM64: Enable Amlogic Meson GXBaby platform
Signed-off-by: Olof Johansson <olof@lixom.net>