For $a_n = 4a_{n-1} - 4a_{n-2}$ with $a_0 = 2$ and $a_1 = 8$, the characteristic equation $(r-2)^2 = 0$ gives the general solution $a_n = (c_1 + c_2 n) \cdot 2^n$. What are $c_1$ and $c_2$?