ARM: sun8i: a83t: Set clock accuracy for 24MHz oscillator

The datasheets for Allwinner SoCs set strict requirements on the
stability of the external crystal oscillators. Add the accuracy
for the main 24MHz oscillator to the device tree.

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