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/octeontx_81xx_defconfig b/configs/octeontx_81xx_defconfig
index e14957c..2f68f17 100644
--- a/configs/octeontx_81xx_defconfig
+++ b/configs/octeontx_81xx_defconfig
@@ -15,6 +15,7 @@
 CONFIG_DEBUG_UART_CLOCK=24000000
 CONFIG_DEBUG_UART=y
 CONFIG_AHCI=y
+CONFIG_SYS_LOAD_ADDR=0x2800000
 CONFIG_FIT=y
 CONFIG_FIT_SIGNATURE=y
 CONFIG_SUPPORT_RAW_INITRD=y