drm/amd/display: Fixed comments (uniform style)

[WHY]
This change was implemented because the comment style was not uniform
across the file. In some lines comments were initiated with // and in
others they were in between /* ... */.
Additionally, the style for multi-line comments was also not uniform and
some comment lines were missing the space between the opening /* and the
first word of the comment.

[HOW]
All comments are now in between /*.../*, multi line comments also use
/*...*/ and for every comment there is now a space between the opening
/* and the first word of the comment.

Signed-off-by: Felipe <Felipe.Clark@amd.com>
Acked-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>