dt-bindings: i2c: apple,i2c: allow multiple compatibles

The intention was to have a SoC-specific and base compatible string
to allow forward compatibility and SoC specific quirks,

Fixes: df7c4a8c ("dt-bindings: i2c: Add Apple I2C controller bindings")
Signed-off-by: Janne Grunau <j@jannau.net>
Cc: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Sven Peter <sven@svenpeter.dev>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Tested-by: Hector Martin <marcan@marcan.st>
Acked-by: Wolfram Sang <wsa@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hector Martin <marcan@marcan.st>