PCI: qcom: Use bitfield definitions for register fields

To maintain uniformity throughout the driver and also to make the code
easier to read, let's make use of bitfield definitions for register fields.

Link: https://lore.kernel.org/r/20230316081117.14288-5-manivannan.sadhasivam@linaro.org


Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>