arm64: defconfig: enable basic boot for Amlogic meson

Enables basic arch and serial console support for Amlogic meson family
SoCs.

Tested with Amlogic P200 and Hardkernel ODROID-C2 boards.

Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>