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/bitmain_antminer_s9_defconfig b/configs/bitmain_antminer_s9_defconfig
index 299206e..79cff75 100644
--- a/configs/bitmain_antminer_s9_defconfig
+++ b/configs/bitmain_antminer_s9_defconfig
@@ -16,6 +16,7 @@
 CONFIG_DEBUG_UART=y
 CONFIG_SYS_CUSTOM_LDSCRIPT=y
 CONFIG_SYS_LDSCRIPT="arch/arm/mach-zynq/u-boot.lds"
+CONFIG_SYS_LOAD_ADDR=0x0
 CONFIG_FIT=y
 CONFIG_FIT_SIGNATURE=y
 CONFIG_FIT_VERBOSE=y