Fix tests for devices that don't have drm@1.2 services

This CL fixes a null pointer dereference that is triggered
when VtsHalDrmV1_2TargetTest is run on a device that
doesn't implement a drm@1.2 vendor service, for any
drm scheme where a vts vendor module is provided. In this
case the test will be skipped.

test: VtsHalDrmV1_2TargetTest

bug:145965256
Change-Id: I43c87db9b560d2024c0fb15cd44d106067ed48ae