arm64: dts: hi6220: Move board data from the dwmmc nodes to hikey dts

Move the board specific descriptions for the dwmmc nodes in the hi6220 SoC
dtsi, into the hikey dts as it's there these belongs.

While changing this, let's take the opportunity to drop the use of the
"ti,non-removable" binding for one of the dwmmc device nodes, as it's not a
valid binding and not used. Drop also the unnecessary use of "num-slots =
<0x1>" for all of the dwmmc nodes, as there is no need to set this since
when default number of slots is one.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>