arm: zynq: Enable DM_GPIO when needed

There are two reasons for doing this change.
There is still !DM driver for xilinx soft gpio IP and especially it is
saving some space for memory constrained boards like cse (almost ~400B).

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/zynq_zc702_defconfig b/configs/zynq_zc702_defconfig
index 1d09701..2c38f00 100644
--- a/configs/zynq_zc702_defconfig
+++ b/configs/zynq_zc702_defconfig
@@ -46,6 +46,7 @@
 CONFIG_DFU_MMC=y
 CONFIG_DFU_RAM=y
 CONFIG_FPGA_XILINX=y
+CONFIG_DM_GPIO=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_ZYNQ=y
 CONFIG_SPI_FLASH=y