arm64: zynqmp: Call psu_init() only when ZYNQMP_PSU_INIT_ENABLED

Remove SPL_BUILD dependency from zynqmp.c and move it to header file.
Use only one symbol for including psu_init.

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

include/configs/xilinx_zynqmp.h

@@ -80,6 +80,10 @@
 # define CONFIG_MTD_DEVICE
 #endif
 
+#if defined(CONFIG_SPL_BUILD)
+#define CONFIG_ZYNQMP_PSU_INIT_ENABLED
+#endif
+
 /* Miscellaneous configurable options */
 #define CONFIG_SYS_LOAD_ADDR		0x8000000