96boards: fix the dragonboard example

[piso77]

These are the minimum changes required to generate a kernel snap that boots on a Dragonboard410c board.

CONFIG_MMC*: to avoid hanging during boot when initrd can't find a valid /dev/disk... paritition

CONFIG_EXT4: the is self explanatory

CONFIG_BLK_DEV_LOOP: to avoid a "can't mount loop device: no space left on device" error on boot

Tested on my dragonbroard, generating a new image from scratch.

Signed-off-by: Paolo Pisati paolo.pisati@canonical.com

Thanks for helping us make a better Snapcraft!

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  https://bugs.launchpad.net/snapcraft/
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  replace it here:

LP: #BUG_NUMBER

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  CONTRIBUTING.md