ath10k: add ath10k_pci_diag_* helpers

ath10k_pci_diag_read32() is for reading u32 from a device and ath10k_pci_diag_read_hi()
is a helper for reading data using "host interest" table.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>