dt-bindings: clock: u8500: Add clkout clock bindings

This adds device tree bindings for the externally routed clocks
CLKOUT1 and CLKOUT2 clocks found in the DB8500.

Cc: devicetree@vger.kernel.org
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220414221751.323525-2-linus.walleij@linaro.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>