ath10k: pull reusable code from pci probe and remove for ahb

Some of the code present in ath10k_pci_{probe|remove} are reusable
in ahb case too. To avoid code duplication, move reusable code to
new functions. Later, those new functions can be called from ahb
module's probe and exit functions.

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