ARM: zynq: Switch to single zynq configurations

There are a lot of zynq configurations which can be merged together and use
only one for all. The similar change has been done for ZynqMP by commit
be1b6c32d9 ("arm64: zynqmp: Use zynqmp_virt platform")

Build SPL with u-boot.img for zc706 like this.
export DEVICE_TREE=zynq-zc706 && make xilinx_zynq_virt_defconfig && make -j8
u-boot.img is generic for all boards.

Tested on Zybo, zc702, zc706, zc770-xm011-x16, cc108 and microzed.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

.travis.yml

@@ -504,13 +504,13 @@ matrix:
           BUILDMAN="^qemu-x86_64$"
           TOOLCHAIN="i386"
           BUILD_ROM="yes"
-    - name: "test/py zynq_zc702"
+    - name: "test/py xilinx_zynq_virt"
       env:
-        - TEST_PY_BD="zynq_zc702"
+        - TEST_PY_BD="xilinx_zynq_virt"
           TEST_PY_TEST_SPEC="not sleep"
           QEMU_TARGET="arm-softmmu"
           TEST_PY_ID="--id qemu"
-          BUILDMAN="^zynq_zc702$"
+          BUILDMAN="^xilinx_zynq_virt$"
     - name: "test/py xilinx_versal_virt"
       env:
         - TEST_PY_BD="xilinx_versal_virt"