Make internal functions static to prevent namespace pollution
Simple DMA allocator that allocates precisely 1 page at a time
Make libsel4utils thread creation more extensible by providing an optional config struct
trivial: style
Improve page_dma allocator to support multiple page allocations
Use standard printf format macros.

Closes SELFOUR-203
Merge pull request #14 from mfernandez/SELFOUR-203

Use standard printf format macros.
Fix error handling in `dma_alloc`.

This code previously was oblivious to a potential malloc failure and tried to
operate on a potentially uninitiliased variable. Found by Goanna.
Fix failure check in `create_reservations`.

I have modified this code to do what I presume the original author intended.
Otherwise this makes no sense, checking a variable for NULL after we've already
dereferenced it. Found by Goanna.
Fix missing error case in `sel4utils_get_cs_vspace`.

Found by Goanna.
Merge pull request #15 from mfernandez/goanna

Miscellaneous fixes based on errors found by Goanna.