The existing uAPI documentation does not adequately describe how the kernel
handles the case where the underlying hardware or driver does not support
the requested configuration.

Add a Configuration Support section describing that behaviour to both the
v1 and v2 documentation, and better document the errors returned where the
requested configuration cannot be supported.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>