arm64: zynqmp: Remove additional gpio header from dlc21

This header shouldn't be in this file and there is already pointer to
dt-bindings/gpio/gpio.h.

Fixes: d2d14383 ("arm64: zynqmp: Add support for DLC21 (Smartlynq+) board")
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/266bc91073f1149f3f60b1c9c0ba509c48470e2e.1644911870.git.michal.simek@xilinx.com