context_hub: Define target version bytes

Define that the first two previously-reserved bytes in the nanoapp
header are used to indicate the target CHRE API version.

Bug: 64852297
Test: run CHQTS on Nanohub, rebuild test app targeting 1.2 and confirm
      it's interpreted correctly
Change-Id: I0582f718bb641cc9c4e1f013578dc2dd50e6d3ec
1 file changed