PCI: qcom: Expose link transition counts via debugfs

Qualcomm PCIe controllers have debug registers in the MHI region that
count PCIe link transitions. Expose them over debugfs to userspace to
help debug the low power issues.

Note that even though the registers are prefixed as PARF_, they don't
live under the "parf" register region. The register naming is following
the Qualcomm's internal documentation as like other registers.

While at it, let's arrange the local variables in probe function to follow
reverse XMAS tree order.

Link: https://lore.kernel.org/r/20230316081117.14288-20-manivannan.sadhasivam@linaro.org


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