ARM: dts: sunxi: h3/h5: Add clock accuracy for external oscillators

The H3 datasheet specifies a tolerance range for the external
oscillators used. Add them to the device tree as the clock accuracy.
The internal oscillator is left unchanged, as it will be removed later.

Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>