arm64: zynqmp: Add gpio labels for modepin

Using labels helps with better identifications of chips.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/15b0f68077fb3c86d438caf8562de87367361c60.1652262769.git.michal.simek@amd.com