An open-label, single arm study to evaluate the week 48 efficacy and safety of a two-drug regimen of Dolutegravir/Lamivudine (DTG/3TC) as a fixed dose combination (FDC), in antiretroviral therapy (ART)-naive HIV-1-infected adolescents, ≥ 12 to < 18 years of age who weigh at least 40 kg