Add the metalava_enabled property

The new property is added for supporting metalava. But some sdk library
cannot use metalava. So "metalava_enabled: false" is added to these
modules.

Test: make -j
Test: checkapi
Merged-In: I334402a69e25f9d32cebe07c1f51a133cd8e966e
Change-Id: I334402a69e25f9d32cebe07c1f51a133cd8e966e
(cherry picked from commit d258f639)