ath10k: Add optional qdss clk

The WiFi firmware found on sm8150 requires that the QDSS clock is
ticking in order to operate, so add an optional clock to the binding to
allow this to be specified in the sm8150 dts and add the clock to the
list of clocks in the driver.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>