Add option to allow product makefiles to skip building super_empty.img

This change doesn't change the condition for building super_empty.img,
it just add a toggle PRODUCT_BUILD_SUPER_EMPTY_IMAGE that product
makefiles can use to skip building super_empty.img.
Products that don't use super_empty at all, for example GSI, can set
this option to ensure the super_empty.img is not built.

Bug: 183068624
Test: "m dist" on GSI and check the build artifacts under OUT and DIST
  directories, and check the contents of *-img-*.zip
Change-Id: I54943952873d2d297fd9d18cbe14742bc12ae9c6