Documentation: Add EFI documentation ...

This adds documentation for the upcoming barebox on EFI support.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: Fix glossary entry, "FTD" -> "FDT" ...

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: Add new sphinxs docs ...

This is a rewrite of the Documentation in reStructuredText format using
Sphinx as build system, see http://sphinx-doc.org/.

The documentation is built into static html pages with 'make docs'.
The pages can be found under Documentation/html after building.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>