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/boston64r2el_defconfig b/configs/boston64r2el_defconfig
index c8da92f..267c817 100644
--- a/configs/boston64r2el_defconfig
+++ b/configs/boston64r2el_defconfig
@@ -12,6 +12,7 @@
 # CONFIG_MIPS_BOOT_ENV_LEGACY is not set
 CONFIG_MIPS_BOOT_FDT=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_LOAD_ADDR=0xffffffff88000000
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_FIT_BEST_MATCH=y