conf/layer: Enable size optimization

because right now the rootfs space for the Nitrogen8MM
is not sufficient for updating meta-balena.

Changlog-entry: conf/layer: Enable full size optimization
Signed-off-by: Alexandru Costache <alexandru@balena.io>

layers/meta-balena-fsl-arm/conf/layer.conf

@@ -42,6 +42,7 @@ SERIAL_CONSOLES:imx8mm-lpddr4-evk = "115200;ttymxc1"
 
 FIRMWARE_COMPRESSION:nitrogen8mm ?= "1"
 FIRMWARE_COMPRESSION:imx8mm-lpddr4-evk ?= "1"
+FULL_OPTIMIZATION = "-Os -pipe ${DEBUG_FLAGS}"
 
 # Temporarily removed until the solidrun upstream repo adds honister support: https://github.com/SolidRun/meta-solidrun-solidsense/issues/2
 BBMASK += "meta-balena-fsl-arm/recipes-bsp/u-boot/u-boot-solidsense-imx6_%.bbappend"