dtc: Make many functions 'static'

[Jon Loeliger]

> This patch marks various functions not shared between c files
> 'static', as they should be.  There are a couple of functions in dtc,
> and many in the testsuite.
> 
> This is *almost* enough to enable the -Wmissing-prototypes warning.
> It's not quite enough, because there's a mess of junk in the flex
> generated code which triggers that warning which I'm not yet sure how
> to deal with.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

jdl