[PATCH v2] sdcard_image: Helper class to create SD Card images

Used for a few weeks now with minor modification for BeagleBoard release images

Signed-off-by: Joel A Fernandes <joelagnel@ti.com>

Please forgive the incorrect subject line, this is for "meta-ti"

This looks good, i think it would be more valuable if it could be
generalized more. I don't claim to be qualified to make the
modifications but would like to provide encouragement to someone else
in the community.

Gavin S