axolotl: specify GMS and mainline modules makefile

Explicitly set MAINLINE_MODULES_MAKEFILE to the default value
to enforce checking the makefile existance.

Disable it for now though, until mainline modules are in a better
state for S.

Change-Id: I333dd57ce64b168bb7ed21b716cbe0efd6db8bfb
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>