Rename boot_info

struct boot_info is named that for historical reasons, and isn't
particularly meaningful.  Essentially it contains all the information -
in "live" form from a single dts or dtb file.  As we move towards support
for dynamic dt overlays, that name will become increasingly bad.

So, in preparation, rename it to dt_info.  At the same time rename the
'the_boot_info' global to 'parser_output' since that's its actual purpose.
Unfortunately we do need the global unless we switch to bison's re-entrant
parser extensions, which would introduce its own complications.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>