ath10k: delay device access after cold reset

It is observed that during cold reset pcie access right
after a write operation to SOC_GLOBAL_RESET_ADDRESS causes
Data Bus Error and system hard lockup. The reason
for bus error is that pcie needs some time to get
back to stable state for any transaction during cold reset. Add
delay of 20 msecs after write of SOC_GLOBAL_RESET_ADDRESS
to fix this issue. This patch is tested on QCA988X. This is
also tested on QCA99X0 which is WIP.

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>