[coreboot] Documentation fixes

[Myles Watson]

Most of the changes here are trivial, but the white space changes would be
harder to undo than to do over.

I changed all groups of 8 spaces to tabs, then all tabs to two spaces so
more of the device tree fits on the page.  It could have been three or
possibly four, but the largest indents I found were 6 tabs, so 4 is a lot of
the space on the page.

Signed-off-by: Myles Watson

Thanks,
Myles