cp2112: driver for the namesake GPIO and I2C master gadget

Documentation:
- CP2112 Datasheet
  https://www.silabs.com/documents/public/data-sheets/cp2112-datasheet.pdf
- AN495: CP2112 Interface Specification
  https://www.silabs.com/documents/public/application-notes/an495-cp2112-interface-specification.pdf
- CP2112 Errata
  https://www.silabs.com/documents/public/errata/cp2112-errata.pdf

The logic is implemented as three sub-drivers.
The parent driver claims the USB device and creates two child devices.
One acts as a GPIO controller and the other is an I2C controller.

Tested with CP2112 revision F02.
Both features seem to work.
HTU21 sensor was used as an I2C slave.

Reviewed by:	adrian, hselasky
MFC after:	2 weeks
Relnotes:	maybe
Differential Revision: https://reviews.freebsd.org/D25359

sys/conf/files

@@ -3331,6 +3331,7 @@ dev/usb/serial/usb_serial.c 	optional ucom | u3g | uark | ubsa | ubser | \
 #
 # USB misc drivers
 #
+dev/usb/misc/cp2112.c		optional cp2112
 dev/usb/misc/ufm.c		optional ufm
 dev/usb/misc/udbp.c		optional udbp
 dev/usb/misc/ugold.c		optional ugold

sys/modules/usb/Makefile

@@ -50,6 +50,7 @@ SUBDIR += ${_rum} ${_run} ${_runfw} ${_uath} upgt usie ural ${_zyd} ${_urtw}
 SUBDIR += atp cfumass uhid uhid_snes ukbd ums udbp ufm uep wmt wsp ugold uled
 SUBDIR += ucom u3g uark ubsa ubser uchcom ucycom ufoma uftdi ugensa uipaq ulpt \
 	  umct umcs umodem umoscom uplcom uslcom uvisor uvscom
+SUBDIR += cp2112
 SUBDIR += udl
 SUBDIR += uether aue axe axge cdce cdceem cue ${_kue} mos rue smsc udav uhso \
 	  ipheth

sys/modules/usb/cp2112/Makefile

@@ -0,0 +1,37 @@
+#
+# $FreeBSD$
+#
+# Copyright (c) Andriy Gapon <avg@FreeBSD.org>
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+
+S=     ${SRCTOP}/sys
+
+.PATH: $S/dev/usb/misc
+
+KMOD=	cp2112
+SRCS=	cp2112.c
+SRCS+=	opt_bus.h opt_usb.h
+SRCS+=	device_if.h bus_if.h gpio_if.h iicbus_if.h usb_if.h usbdevs.h
+
+.include <bsd.kmod.mk>