drm: Renaming DP training vswing pre emph defines

Adding new defines, older one will be removed in the last patch in the series.
This is to rename the defines to have levels instead of values for vswing and
pre-emph levels as the values may differ in other scenarios like low vswing of
eDP1.4 where the values are different.

Done using following cocci patch for each define:
@@
@@

 # define DP_TRAIN_VOLTAGE_SWING_400     (0 << 0)
+ # define DP_TRAIN_VOLTAGE_SWING_LEVEL_0     (0 << 0)

...
Cc: dri-devel@lists.freedesktop.org

Signed-off-by: Sonika Jindal <sonika.jindal@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>