Convert CONFIG_SYS_LOAD_ADDR to Kconfig

Now that we have consistent usage, migrate this symbol to Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/configs/xilinx_zynqmp_mini_qspi_defconfig b/configs/xilinx_zynqmp_mini_qspi_defconfig
index 5d65371..b2ffecf 100644
--- a/configs/xilinx_zynqmp_mini_qspi_defconfig
+++ b/configs/xilinx_zynqmp_mini_qspi_defconfig
@@ -12,6 +12,7 @@
 # CONFIG_CMD_ZYNQMP is not set
 # CONFIG_PSCI_RESET is not set
 # CONFIG_EXPERT is not set
+CONFIG_SYS_LOAD_ADDR=0x8000000
 # CONFIG_LEGACY_IMAGE_FORMAT is not set
 # CONFIG_AUTOBOOT is not set
 # CONFIG_DISPLAY_CPUINFO is not set