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/socfpga_stratix10_defconfig b/configs/socfpga_stratix10_defconfig
index c352c45..7534f25 100644
--- a/configs/socfpga_stratix10_defconfig
+++ b/configs/socfpga_stratix10_defconfig
@@ -16,6 +16,7 @@
 # CONFIG_PSCI_RESET is not set
 CONFIG_OPTIMIZE_INLINING=y
 CONFIG_SPL_OPTIMIZE_INLINING=y
+CONFIG_SYS_LOAD_ADDR=0x02000000
 CONFIG_BOOTDELAY=5
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="earlycon"