arm64: dts: apple: Add missing M1 (t8103) devices

This adds support for following Apple M1 devices:
 - MacBook Pro (13-inch, M1, 2020)
 - MacBook Air (M1, 2020)
 - iMac (24-inch 2021)

Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Signed-off-by: Janne Grunau <j@jannau.net>
Tested-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Hector Martin <marcan@marcan.st>