We shouldn't reference Linux kernel functions or Linux itself in proper
bindings. It's OK to reference functions in the kernel when explaining
examples, but otherwise we shouldn't reference functions to describe
what the binding means.

Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Rob Herring <robh@kernel.org>