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/malta64el_defconfig b/configs/malta64el_defconfig
index cd78b81..27f19cd 100644
--- a/configs/malta64el_defconfig
+++ b/configs/malta64el_defconfig
@@ -7,6 +7,7 @@
 CONFIG_BUILD_TARGET="u-boot-swap.bin"
 CONFIG_SYS_LITTLE_ENDIAN=y
 CONFIG_CPU_MIPS64_R2=y
+CONFIG_SYS_LOAD_ADDR=0xffffffff81000000
 # CONFIG_AUTOBOOT is not set
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_MISC_INIT_R=y