Revert "emulator: Build emulator platform images as ARMv7-A"

This reverts commit c7e3877dad2333bfdf41e99470d559f381431d3c.

I can't get the emulator to run it, so we go back to good old ARMv6.
Shakira is ARMv6 anyways, so no reason to test the ARMv7 codepaths.
Build 2D Gallery by default

Change-Id: Ieef62cd1c6dd4eec3e26c0fd0e336afa98ba29aa