ubifs: Add configuration for space-fixup

[ee-smuxel]

Allows passing the '-F' flag to force file-system free space to be fixed up on first mount.

[michaelolbrich]

Hmm, I'm not entirely opposed to this, but why not just use extraargs for this?

[ee-smuxel]

You could argue with any argument that it could be passed with extraargs to be fair.

I think it's worth an options as it's the recommended way of generating a UBIFS image when one can not flash it through ubiformat which is a common-ish case. It's also one of the options specifically talked about in the mtd-linux FAQ: http://linux-mtd.infradead.org/faq/ubifs.html#L_free_space_fixup.

[michaelolbrich]

Ok, that sounds like the option is prominent enough to deserve its own property here.