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_rv32_spl_defconfig b/configs/ae350_rv32_spl_defconfig
index 34c6af6..e2c20fa 100644
--- a/configs/ae350_rv32_spl_defconfig
+++ b/configs/ae350_rv32_spl_defconfig
@@ -8,6 +8,7 @@
 CONFIG_TARGET_AX25_AE350=y
 CONFIG_RISCV_SMODE=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_LOAD_ADDR=0x100000
 CONFIG_FIT=y
 CONFIG_SPL_LOAD_FIT_ADDRESS=0x00200000
 CONFIG_BOOTDELAY=3