MAINTAINERS: arm: apple: Add Janne as maintainer

Sven and I have agreed to share the maintainership for the ARM/APPLE
platform after Marcan's step down. I'm handling the downstream Asahi
Linux tree since April 2024 and worked on or wrote several drivers for
the platform.

Signed-off-by: Janne Grunau <j@jannau.net>
Acked-by: Sven Peter <sven@svenpeter.dev>
Acked-by: Hector Martin <marcan@marcan.st>
Acked-by: Neal Gompa <neal@gompa.dev>
Link: https://lore.kernel.org/r/20250208-maint-soc-apple-v1-1-a7f7337baec0@jannau.net


Signed-off-by: Arnd Bergmann <arnd@arndb.de>