dt-bindings: soc: remove obsolete zte zx header

The zte zx platform had been removed in commit 89d4f98 ("ARM: remove
zte zx platform"), so this header is no longer needed.

Cc: Arnd Bergmann <[email protected]>
Cc: Jun Nie <[email protected]>
Cc: Shawn Guo <[email protected]>
Signed-off-by: Zenghui Yu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Rob Herring <[email protected]>

Author: Zenghui Yu