arm64: allwinner: h5: Remove syslink to shared DTSI

The arm64 H5 and arm H3 SoCs share roughly the same base, and therefore
share a significant part of their device tree.

The approach we took was to add a symlink from the arm64 DTSI to the arm
DTSI.

Now that the arm DT folder is exposed in the include path, we can just use
it and remove our symlink.

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