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/topic_miami_defconfig b/configs/topic_miami_defconfig
index e9e03a2..b43e546 100644
--- a/configs/topic_miami_defconfig
+++ b/configs/topic_miami_defconfig
@@ -18,6 +18,7 @@
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_SYS_CUSTOM_LDSCRIPT=y
 CONFIG_SYS_LDSCRIPT="arch/arm/mach-zynq/u-boot.lds"
+CONFIG_SYS_LOAD_ADDR=0x0
 CONFIG_BOOTDELAY=0
 CONFIG_USE_PREBOOT=y
 CONFIG_SPL_STACK_R=y