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/grpeach_defconfig b/configs/grpeach_defconfig
index e4a570d..1a6811f 100644
--- a/configs/grpeach_defconfig
+++ b/configs/grpeach_defconfig
@@ -9,6 +9,7 @@
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="r7s72100-gr-peach-u-boot"
 CONFIG_RZA1=y
+CONFIG_SYS_LOAD_ADDR=0x20400000
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="ignore_loglevel"