clk: sunxi-ng: sun8i: a83t: Add /2 fixed post divider to audio PLL

On the A83T, the audio PLL should have its div1 set to 0, or /1, and
div2 set to 1, or /2. This setting is the default, and is required
to match the sigma-delta modulation parameters from the BSP kernel.

This patch adds a /2 fixed post divider to the audio PLL, and fixes
the enforced d1 & d2 values. This also resolves the mismatch between
the values mentioned in the comment for the audio PLL, and the actual
enforced values.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>