HWC2: Change version detection scheme

SurfaceFlinger now checks hardware composer module numbers by looking
at device.version, the high byte of which corresponds to the HWC
major version (0x01... for HWC 1.x and 0x02... for HWC 2.0).

Bug: 28161397
Change-Id: I4560bf60c35bdb97629fda1aa1256b03122688ad