ath10k: disable cpuidle during downloading firmware

Downloading ath10k firmware needs a large number of IOs and
cpuidle's miss predictions make it worse. In the worst case,
resume time can be three times longer than the average on sdio.

This patch disables cpuidle during firmware downloading by
applying PM_QOS_CPU_DMA_LATENCY in ath10k_download_fw().

Tested-on: QCA9880
Tested-on: QCA6174 hw3.2 SDIO WLAN.RMH.4.4.1-00029

Signed-off-by: Ikjoon Jang <ikjn@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>