ARM: renesas: Enable LTO on R-Car3 ULCB

Enable LTO (link time optimization) to improve optimization
and reduce code size by cca. 31 kiB.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
diff --git a/configs/rcar3_ulcb_defconfig b/configs/rcar3_ulcb_defconfig
index 43361a2..076bc2d 100644
--- a/configs/rcar3_ulcb_defconfig
+++ b/configs/rcar3_ulcb_defconfig
@@ -13,6 +13,7 @@
 CONFIG_RCAR_GEN3=y
 CONFIG_TARGET_ULCB=y
 CONFIG_SYS_LOAD_ADDR=0x58000000
+CONFIG_LTO=y
 CONFIG_REMAKE_ELF=y
 CONFIG_SYS_MONITOR_LEN=1048576
 CONFIG_FIT=y