configs: imx6dl_mamoj_defconfig: Enable LTO on imx6dl_mamoj board

configs: imx6dl_mamoj_defconfig: Enable LTO on imx6dl_mamoj board

Enable LTO on mamoj to reduce SPL and uboot size. Tested with gcc
gcc-11.1.0

U-Boot 2022.04-rc4-00051-g17fc5facd0 (Mar 23 2022 - 16:43:43 +0100)

CPU:   Freescale i.MX6DL rev1.3 996 MHz (running at 792 MHz)
CPU:   Extended Commercial temperature grade (-20C to 105C) at 40C
Reset cause: POR
Model: BTicino i.MX6DL Mamoj board
DRAM:  512 MiB
Core:  29 devices, 12 uclasses, devicetree: separate
MMC:   FSL_SDHC: 2
Loading Environment from MMC... OK
In:    serial
Out:   serial
Err:   serial
Net:
Error: ethernet@2188000 address not set.
No ethernet found.

Tested-by: Raffaele RECALCATI <raffaele.recalcati@bticino.it>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>