Convert mp() to dprintf()

Convert mp() to dprintf()

There's only one function required for printing debugging information
and that is dprintf() - there is no need to invent another. dprintf()
is also superior to mp() because it can be enabled/disabled on a
per-file basis via the DEBUG symbol.

Switch all users of mp() to dprintf() and leave them disabled (don't
define the DEBUG) so we have a less verbose boot by default.

Signed-off-by: Matt Fleming <matt.fleming@linux.intel.com>