SF: Use PNP ID + Product ID for modelString fallback

Use PNP ID and Product ID as the fallback to Display Name for modelString. The PNP ID is in block zero of the EDID and is validated earlier in the function. This guarantees EDIDs without a Monitor Name Descriptor Block will have a valid modelString.

Bug: 419618180
Flag: EXEMPT bugfix
Test: DisplayIdentificationTest.parseEdid
Test: Tested on device without Monitor Name Descriptor Block, ensured parseEdid now succeeds

Change-Id: Ibf0377dce80ff03c648fcd3411e676a74796a073