WIP: HID: Add hid-appleft for Apple Macbook Trackpads

To be used with the SPI HID transport.

Based on input/keyboard/applespi.c and hid-magicmouse.c. bcm5974.c uses
the report format.

Could possible integrated into hid-magicmouse but that would a
refactoring since the integrated Trackpad uses Report Id 2 as the the
USB variant of the magic Trackpad 2. The report fromat is completly
different.

Both bcm5974 and applespi support the same report format. applespi could
be deprecated once the SPI HID tansport gains ACPI support. bcm5974.c
could probably be converted to HID using hid-appleft.

drivers/hid/Kconfig

@@ -147,6 +147,18 @@ config HID_APPLEIR
 
 	Say Y here if you want support for Apple infrared remote control.
 
+config HID_APPLEFT
+	tristate "Apple Force Touch Trackpad multi-touch support"
+	depends on HID
+	help
+	Support for the Apple Fource Touch Trackpad multi-touch.
+
+	This driver supports the multi-touch and pressure measure features of
+	the trackpad found on Apple MacBooks staring in 2015.
+
+	Say Y here if you want support for the multi-touch features of the
+	Fource Touch Trackpad on Apple MacBooks.
+
 config HID_ASUS
 	tristate "Asus"
 	depends on USB_HID

drivers/hid/Makefile

@@ -27,6 +27,7 @@ obj-$(CONFIG_HID_ALPS)		+= hid-alps.o
 obj-$(CONFIG_HID_ACRUX)		+= hid-axff.o
 obj-$(CONFIG_HID_APPLE)		+= hid-apple.o
 obj-$(CONFIG_HID_APPLEIR)	+= hid-appleir.o
+obj-$(CONFIG_HID_APPLEFT)	+= hid-appleft.o
 obj-$(CONFIG_HID_CREATIVE_SB0540)	+= hid-creative-sb0540.o
 obj-$(CONFIG_HID_ASUS)		+= hid-asus.o
 obj-$(CONFIG_HID_AUREAL)	+= hid-aureal.o