ath11k: enable internal sleep clock

On x86 and other non-qcom platforms, host needs to explicitly tell the firmware
to use the internal sleep clock. Some QCA6390 modules have OTP burnt with
external sleep clock selected, and these modules can't work expectedly unless
firmware selects internal sleep clock.

Add a field to hw_params to support this difference.

Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1
Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.1.0.1-01238-QCAHKSWPL_SILICONZ-2

Signed-off-by: Carl Huang <cjhuang@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1597389030-13887-11-git-send-email-kvalo@codeaurora.org