ARM: zynq: Simplify zynq configuration

Extending Kconfig for adding new platform is a lot of work
for nothing. Setting SYS_CONFIG_NAME directly in Kconfig and
remove all dependencies on TARGET_ZYNQ_* options including SPL.
As a side-effect it also remove custom init folder for ps7_init_gpl.*
files. Folder is chosen based on device-tree file.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/zynq_zc702_defconfig b/configs/zynq_zc702_defconfig
index 052679a..e1b1fc9 100644
--- a/configs/zynq_zc702_defconfig
+++ b/configs/zynq_zc702_defconfig
@@ -1,4 +1,5 @@
 CONFIG_ARM=y
+CONFIG_SYS_CONFIG_NAME="zynq_zc70x"
 CONFIG_ARCH_ZYNQ=y
 CONFIG_DEFAULT_DEVICE_TREE="zynq-zc702"
 CONFIG_SPL=y