ARM: at91/defconfig: add the XDMA driver

Add the Atmel eXtended DMA Controller driver option. This driver is first used
on SAMA5D4 SoCs and only relevant in sama5_defconfig file.
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/configs/sama5_defconfig

@@ -178,6 +178,7 @@ CONFIG_LEDS_TRIGGER_GPIO=y
 CONFIG_RTC_CLASS=y
 CONFIG_RTC_DRV_AT91RM9200=y
 CONFIG_DMADEVICES=y
+CONFIG_AT_XDMAC=y
 # CONFIG_IOMMU_SUPPORT is not set
 CONFIG_IIO=y
 CONFIG_AT91_ADC=y