board: tbs2910: Enable Link Time Optimizations in defconfig

This saves about 12 kBytes image size and helps to stay within the
size limit.

Suggested-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Soeren Moch <smoch@web.de>
diff --git a/configs/tbs2910_defconfig b/configs/tbs2910_defconfig
index e1278f2..8a33160 100644
--- a/configs/tbs2910_defconfig
+++ b/configs/tbs2910_defconfig
@@ -14,6 +14,7 @@
 CONFIG_PRE_CON_BUF_ADDR=0x7c000000
 CONFIG_CMD_HDMIDETECT=y
 CONFIG_AHCI=y
+CONFIG_LTO=y
 CONFIG_SUPPORT_RAW_INITRD=y
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTCOMMAND=y