Rename care map in pb format to care_map.pb

The new suffix distinguishes the new care_map from the ones in plain
text format; and thus the old update_verifier won't report an error
upon parsing failures.

Bug: 115740187
Test: Generate OTA files for Pixels
Change-Id: Ia782afd8cbb0f4bb8c363edaa00e92ab302d5d1b