This driver provides support for multiple HID driver attachments
to single HID transport backend. This ability existed in Net/OpenBSD
(uhidev and ihidev drivers) but has never been ported to FreeBSD.
Unlike Net/OpenBSD we do not use report number alone to distinct report
source but we follow MS way and use a top level collection (TLC) usage
index that report belongs to as a location key.
The driver performs child device autodiscovery based on HID report
descriptor data, proxying of HID requests from child devices to parent
transport backends and broadcasting of interrupts in backward direction.
Differential revision: https://reviews.freebsd.org/D27888
