Implement Linux I2C ioctl translation in the Linux compatibility layer
and wire iicbus cdevs up for in-kernel rdwr handling.
Support common i2c-dev requests including SLAVE, FUNCS, and RDWR,
while rejecting unsupported 10-bit and SMBus operations.

Signed-off-by:	YAO, Xin <mr.yaoxin@outlook.com>
Reviewed by:	imp, adrian, pouria
Differential Revision: https://reviews.freebsd.org/D56251

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with:		pfg
MFC After:		3 days
Sponsored by:		Netflix

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Also check the return value of copyin(9) to prevent unnecessary allocation in the failure case.

Submitted by:	ngie
Reviewed by:	kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D5155

--Allow multiple open iic fds by storing addressing state in cdevpriv
--Fix, as much as possible, the baked-in race conditions in the iic
ioctl interface by requesting bus ownership on I2CSTART, releasing it on
I2CSTOP/I2CRSTCARD, and requiring bus ownership by the current cdevpriv
to use the I/O ioctls
--Reduce internal iic buffer size and remove 1K read/write limit by
iteratively calling iicbus_read/iicbus_write
--Eliminate dynamic allocation in I2CWRITE/I2CREAD
--Move handling of I2CRDWR to separate function and improve error handling
--Add new I2CSADDR ioctl to store address in current cdevpriv so that
I2CSTART is not needed for read(2)/write(2) to work
--Redesign iicbus_request_bus() and iicbus_release_bus():
    --iicbus_request_bus() no longer falls through if the bus is already
owned by the requesting device.  Multiple threads on the same device may
want exclusive access.  Also, iicbus_release_bus() was never
device-recursive anyway.
    --Previously, if IICBUS_CALLBACK failed in iicbus_release_bus(), but
the following iicbus_poll() call succeeded, IICBUS_CALLBACK would not be
issued again
    --Do not hold iicbus mtx during IICBUS_CALLBACK call.  There are
several drivers that may sleep in IICBUS_CALLBACK, if IIC_WAIT is passed.
    --Do not loop in iicbus_request_bus if IICBUS_CALLBACK returns
EWOULDBLOCK; instead pass that to the caller so that it can retry if so
desired.

Differential Revision:	https://reviews.freebsd.org/D2140
Reviewed by:	imp, jhb, loos
Approved by:	kib (mentor)

We should probably fix sys/gpio.h instead.

This lets us call iic(4) ioctls without needing the kernel source code
and follows the same model of GPIO.

MFC after:	3 weeks

allow consumers of iicbus_transfer() to send messages with repeated starts.

Reviewed by:	imp