src/update_handler: support vfat to vfat
src/update_handler: support vfat to vfat

This adds support for writing a .vfat image (which should be a valid
extension for a vfat image) to a vfat slot by using the img_to_fs_handler.

Signed-off-by: Enrico Joerns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

rauc/rauc,jluebbe/rauc,jluebbe/rauc,rauc/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,ejoerns/rauc