Some qcom platforms make some GPIOs or pins unavailable for use
by non-secure operating systems, and thus reading or writing the
registers for those pins will cause access control issues.
Introduce a DT property to describe the set of GPIOs that are
available for use so that higher level OSes are able to know what
pins to avoid reading/writing.

Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: <devicetree@vger.kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Tested-by: Timur Tabi <timur@codeaurora.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>