ARM: zynq: Rename defconfig to be align with ZynqMP and Versal

Just cosmetic change before real switch.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/board/xilinx/zynq/MAINTAINERS b/board/xilinx/zynq/MAINTAINERS
index fc6463a..78bcd84 100644
--- a/board/xilinx/zynq/MAINTAINERS
+++ b/board/xilinx/zynq/MAINTAINERS
@@ -5,3 +5,4 @@
 F:	board/xilinx/zynq/
 F:	include/configs/zynq*.h
 F:	configs/zynq_*_defconfig
+F:	configs/xilinx_zynq_*