SF: Hash and cache descriptor block serial number

More EDID fields are required as a part of migrating to EDID-based
display IDs. This CL parses the device's serial number from the serial
number descriptor bloc, (depicted by the FF marker), hashes it using a
stable hash, and serves it as a part of the Edid struct.

Later, amongst others, this value will be used to fabricate a unique
display ID that is based on the display's EDID.

See:
1. EDID spec: https://glenwing.github.io/docs/VESA-EEDID-A2.pdf
2. https://en.wikipedia.org/wiki/Extended_Display_Identification_Data#Structure,_version_1.4

Flag: com.android.graphics.surfaceflinger.flags.stable_edid_ids
Bug: 378923759
Test: DisplayIdentification_test
Change-Id: If9c9358b0d0850337496740d15419fd0ed330a02