olimex_imx233_olinuxino_defconfig: genimage support

* add a post-image.sh script
* update defconfig for genimage
* update readme.txt

[Peter: also add host-dosfstools dependency for vfat partition]
Signed-off-by: Phil Eichinger <phil@zankapfel.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
4 files changed