arm64: dts: rockchip: Refine nanopi4 differences

The nanopi4 boards differ primarily in their power trees, with the main
5V and 3.3V rails having very different topologies on the smaller USB-C
powered boards vs. the 12V-powered T4, as well as minor variation in
other regulators related to various external connectors.

Additionally, the recovery key is only present on the T4 - ADC_IN1 is
simply pulled high and not exposed on the other boards - and the lowest
common denominator for MMC speed is actually HS200 according to the
vendor DTs.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>