Add atopcase, the Apple HID over SPI input driver

The driver provides support for Human Interface Devices (HID) on
Serial Peripheral Interface (SPI) buses on Apple Intel Macs
produced in 2015-2018.

The driver appears to work more stable after installation of Darwin OSI
in acpi(4) driver.
To install Darwin OSI insert following lines into /boot/loader.conf:

hw.acpi.install_interface="Darwin"
hw.acpi.remove_interface="Windows 2009, Windows 2012"

Reviewed by: wulf
Differential revision: https://reviews.freebsd.org/D39863