arm64: defconfig: enable RK808 components

Many rockchip based arm64 boards use RK808 as PMIC, so
enabe it here let the board bootup normally.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
[added rk808-rtc as module and rk808-clk output built in]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>