vndk-def: Add more output formats to vndk command

This commit adds the --output-format option to vndk command.  When
`make` is specified, VNDK definition tool will fill in the placeholders
in the boilerplates and print a make file to stdout.

Bug: 37867089
Test: ./vndk_definition_tool.py vndk --output-format=make ...
Merged-In: I0185e1690264d0cefafa8536db2e0cf34daaeee0
(cherry picked from commit 5ad8d0fe)

Change-Id: Icb15870b7cd1ef6bb6ab71735ea60230a1b517f1