Add min and max supported versions

Add MIN_PLATFORM_VERSION and MAX_PLATFORM_VERSION to track
the range of releases that are expected to be released from
the current branch.

Also simplify version_defaults.mk by moving most of the code
to envsetup.mk.

Test: build/make/tests/envsetup_tests.sh
Change-Id: I4f19c31c267e202f8f5ba1384a8b4385d725f9d7
(cherry picked from commit c9016593)