MAINTAINERS: Add apple-spi driver & binding files

This Apple SPI controller is present on Apple ARM SoCs (t8103/t6000).

Splitting this change from the binding/driver commits to avoid merge
conflicts with other things touching this section, as usual.

Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Janne Grunau <j@jannau.net>
Link: https://lore.kernel.org/r/20241106-asahi-spi-v5-3-e81a4f3a8e19@jannau.net


Signed-off-by: Sven Peter <sven@svenpeter.dev>