ARM64: zynqmp: Select SYS_CONFIG_NAME via Kconfig

This option enable adding new platform suport just by adding defconfig
and DTS file which will target generic configuration for SoC.
Make no sense to extend Kconfig just create a pointer between DTS and
configuration file.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/xilinx_zynqmp_ep_defconfig b/configs/xilinx_zynqmp_ep_defconfig
index 33f29af..a1f3580 100644
--- a/configs/xilinx_zynqmp_ep_defconfig
+++ b/configs/xilinx_zynqmp_ep_defconfig
@@ -1,4 +1,5 @@
 CONFIG_ARM=y
+CONFIG_SYS_CONFIG_NAME="xilinx_zynqmp_ep"
 CONFIG_ARCH_ZYNQMP=y
 CONFIG_ZYNQMP_USB=y
 CONFIG_SYS_TEXT_BASE=0x8000000