dt-bindings: clock: Update GCC bindings for protected-clocks

Add protected-clocks list which could used to specify the clocks to be
bypassed on certain devices.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>