clk: qcom: gcc-ipq806x: add unusued flag for critical clock

Some clocks are used by other devices present on the SoC. For example
the gsbi4_h_clk is used by RPM and is if disabled cause the RPM to
reject any regulator change command. These clock should never be
disabled.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Tested-by: Jonathan McDowell <noodles@earth.li>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220226135235.10051-9-ansuelsmth@gmail.com