arm64: dts: rockchip: enable HS200 for eMMC on rock64

eMMC that's sold by Pine64 can do HS200, rk3328 can do it
as well, so update DTS to enable it.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>