Add OWNERS for VTS module VtsHalGraphicsMapperV2_0TargetTest

Each VTS module is required to have OWNERS file. The ownership is based on
go/vts-owners. For more information about ownership policy, please visit
go/xts-owners-policy.

Test: Tree Hugger
Bug: 143903671
Change-Id: I6e760696cf6e4e5785ddec4ff8c74c12005ecbae