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/ae350_rv64_defconfig b/configs/ae350_rv64_defconfig
index 05eee37..4e56224 100644
--- a/configs/ae350_rv64_defconfig
+++ b/configs/ae350_rv64_defconfig
@@ -6,6 +6,7 @@
 CONFIG_TARGET_AX25_AE350=y
 CONFIG_ARCH_RV64I=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_LOAD_ADDR=0x100000
 CONFIG_FIT=y
 CONFIG_BOOTDELAY=3
 CONFIG_BOARD_EARLY_INIT_F=y