ath10k: make some of ath10k_pci_* func reusable

Some of static functions present in pci.c file are reusable
in ahb (qca4019) case. Remove static word for those reusable
functions and have those function prototype declaration in
pci.h file. So that, pci.h header file can be included in
ahb module and reused. There is no functionality changes done
in this patch.

Signed-off-by: Raja Mani <rmani@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>