spi: apple: Add driver for Apple SPI controller

Add a driver for the SPI controller integrated on Apple SoCs.
This is necessary to support the keyboard on Apple Silicon laopts
since their keyboard uses an Apple-specific HID over SPI protocol.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested on: Macbook Air M1
Tested-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index d07e9a2..0a6a85f 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -50,6 +50,13 @@
 	  IP core. Please find details on the "Embedded Peripherals IP
 	  User Guide" of Altera.
 
+config APPLE_SPI
+	bool "Apple SPI driver"
+	default y if ARCH_APPLE
+	help
+	  Enable the Apple SPI driver. This driver can be used to
+	  access the SPI flash and keyboard on machines based on Apple SoCs.
+
 config ATCSPI200_SPI
 	bool "Andestech ATCSPI200 SPI driver"
 	help