Documentation: ABI: update gpio-cdev to reference chardev.rst

Update the gpio-cdev interface document to refer to the new
chardev.rst.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

docs: ABI: cleanup several ABI documents

There are some ABI documents that, while they don't generate
any warnings, they have issues when parsed by get_abi.pl script
on its output result.

Address them, in order to provide a clean output.

Reviewed-by: Tom Rix <trix@redhat.com> # for fpga-manager
Reviewed-By: Kajol Jain<kjain@linux.ibm.com> # for sysfs-bus-event_source-devices-hv_gpci and sysfs-bus-event_source-devices-hv_24x7
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> #for IIO
Acked-by: Oded Gabbay <oded.gabbay@gmail.com> # for Habanalabs
Acked-by: Vaibhav Jain <vaibhav@linux.ibm.com> # for sysfs-bus-papr-pmem
Acked-by: Cezary Rojewski <cezary.rojewski@intel.com> # for catpt
Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Ilya Dryomov <idryomov@gmail.com> # for rbd
Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/5bc78e5b68ed1e9e39135173857cb2e753be868f.1604042072.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

gpio: add a userspace character device ABI

Put in some documentation for the new character device ABI
so we can properly etch it in stone.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>