msm: pcie: support configurable number of PARF testbus selectors

The number of PCIe PARF testbus signals available varies for each
PCIe controller version. In order to capture all possible signals
during a PARF dump, add support to define how many PCIe PARF
testbus selectors are provided.

Change-Id: I4d99df6f61b66cbccc3c5e2e7ce6ab2f89db5669
Signed-off-by: Tony Truong <truong@codeaurora.org>