arm64: dts: apple: t8103: Add PMGR nodes

This adds the two PMGR nodes and all known power state subnodes. Since
there are a large number of them, let's put them in a separate file to
include.

Reviewed-by: Sven Peter <sven@svenpeter.dev>
Signed-off-by: Hector Martin <marcan@marcan.st>