ARM64: zynqmp: Use DTS name for different psu_init_gpl* files in SPL

CONFIG_SYS_CONFIG_NAME is not proper config option for different low
level init files because different board revisions requires different
psu_init_gpl* files.

Also at the end of moving drivers to DM all board specific configuration
files should be removed.

The same changes was done for Zynq.
"ARM: zynq: Simplify zynq configuration"
(sha1: ad5b5801)

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

board/xilinx/zynqmp/Makefile

@@ -7,7 +7,7 @@
 
 obj-y	:= zynqmp.o
 
-hw-platform-y :=$(shell echo $(CONFIG_SYS_CONFIG_NAME))
+hw-platform-y :=$(shell echo $(CONFIG_DEFAULT_DEVICE_TREE))
 
 init-objs := $(if $(wildcard $(srctree)/$(src)/$(hw-platform-y)/psu_init_gpl.c),\
 	$(hw-platform-y)/psu_init_gpl.o)