ddr: altera: Make DLEVEL behavior inclusive

Originally, the DLEVEL selects the debug level within the sequencer code,
but only displays the messages on that particular debug level. Tweak the
handling such that for particular debug level, debug messages on that
level and lower are displayed. This allows better regulation of debug
message verbosity.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Chin Liang See <clsee@altera.com>