ath10k: add support to configure channel dwell time

Configure channel dwell time from duration of the scan request
received from mac80211 when the duration is non-zero. When the
scan request does not have duration value, use the default ones,
the current implementation.

Corresponding flag NL80211_EXT_FEATURE_SET_SCAN_DWELL is
advertized.

Supported Chipsets:
 -QCA988X/QCA9887 PCI
 -QCA99X0/QCA9984/QCA9888/QCA4019 PCI
 -QCA6174/QCA9377 PCI/USB/SDIO
 -WCN3990 SNOC

Tested on QCA9984 with firmware ver 10.4-3.6-0010

Signed-off-by: Pradeep Kumar Chitrapu <pradeepc@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>