Encode VmapTable entries offset by 2 to reduce size.

We're using special values 0xffff and 0xfffe for an
fp register marker and for method pointer, respectively.
These values were being encoded as 3 bytes each and
this changes their encoding to 1 byte.

Bug: 9437697
Change-Id: Ic1720e898b131a5d3f6ca87d8e1ecdf76fb4160a