soc/intel/tigerlake: Add soc_get_cpu_rp_vw_idx() function

soc/intel/tigerlake: Add soc_get_cpu_rp_vw_idx() function

The PMC IPC method used to enable/disable PCIe clk sources uses the
LCAP PN field to distinguish PCH RPs. For CPU RPs, the PMC IPC
command expects the RP number to be its "virtual wire index"
instead. This new function returns this virtual wire index
for each of the CPU PCIe RPs.

BUG=b:197983574

Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Change-Id: I7aa14a634dcd90c4817009db970fb209ae02c63d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60179
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Crawford <tcrawford@system76.com>
Reviewed-by: Cliff Huang <cliff.huang@intel.corp-partner.google.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>