ARM: renesas: Enable LTO on R-Car

Enable LTO globally on Renesas R-Car platforms. This has been enabled
on a subset of boards already, but at this point it is safe to enable
it globally. This saves units or tens of kiB from the resulting build.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 6b072be..fde85dc 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1076,6 +1076,7 @@
 	select DM
 	select DM_SERIAL
 	select GPIO_EXTRA_HEADER
+	select LTO
 	imply BOARD_EARLY_INIT_F
 	imply CMD_DM
 	imply FAT_WRITE