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/linkit-smart-7688_defconfig b/configs/linkit-smart-7688_defconfig
index cf2f204..d12f111 100644
--- a/configs/linkit-smart-7688_defconfig
+++ b/configs/linkit-smart-7688_defconfig
@@ -15,6 +15,7 @@
 CONFIG_RESTORE_EXCEPTION_VECTOR_BASE=y
 # CONFIG_MIPS_BOOT_ENV_LEGACY is not set
 CONFIG_MIPS_BOOT_FDT=y
+CONFIG_SYS_LOAD_ADDR=0x80100000
 CONFIG_FIT=y
 CONFIG_FIT_SIGNATURE=y
 CONFIG_LEGACY_IMAGE_FORMAT=y