IMAGE_FSTYPES cleanup

Currently we have varied selection of image types that are built. An analysis of supported targets show:

r-car-m3-starter-kit/r-car-h3-starter-kit

    IMAGE_FSTYPES="tar.gz tar.bz2 ext4"

qemux86-64

    IMAGE_FSTYPES=" tar.bz2 ext4"

minnowboard

    IMAGE_FSTYPES="live wic"

raspberrypi2/raspberrypi3

    IMAGE_FSTYPES="tar.bz2 ext3 rpi-sdimg"

We gain a couple of things by optimizing which images to generate:

• Faster build times as we do not generate images types that are not used
• Storage optimizations in CI pipelines which store build artifacts
• An unified approach across multiple targets

The suggested optimizations are:

r-car-m3-starter-kit/r-car-h3-starter-kit (reference)

    IMAGE_FSTYPES="wic.gz"

qemux86-64

    IMAGE_FSTYPES=" ext4"

minnowboard

    IMAGE_FSTYPES="wic.gz"

raspberrypi2/raspberrypi3 (wks file provided in meta-raspberrypi)

    IMAGE_FSTYPES="wic.gz"

This basically means that we try to "standardize" on the WIC format where possible.