soc: arm: xilinx_zynq7000: add MMU PTEs for all AXI GPIO IP core instances

add the MMU page table entries for all instances of the Xilinx AXI GPIO
controller IP core. Other than any Zynq-7000 peripheral supported so far,
the existance of 1..n instances of the IP core within the FPGA part of the
SoC is optional. Therefore, other than addressing instances of supported
peripherals using their DT node label as has always been the case so far,
the data for the MMU page table is added using the DT_FOREACH_STATUS_OKAY
macro.

Signed-off-by: Immo Birnbaum <Immo.Birnbaum@weidmueller.com>