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/rpi_4_32b_defconfig b/configs/rpi_4_32b_defconfig
index b1503e9..7fb63c1 100644
--- a/configs/rpi_4_32b_defconfig
+++ b/configs/rpi_4_32b_defconfig
@@ -5,6 +5,7 @@
 CONFIG_SYS_MALLOC_F_LEN=0x2000
 CONFIG_ENV_SIZE=0x4000
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_LOAD_ADDR=0x1000000
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_USE_PREBOOT=y
 CONFIG_PREBOOT="pci enum; usb start;"