drm/amd/display: Clean up cursor code

This will also fix disappearing cursor after resume.

With this change we'll set cursor attributes, as well as
cursor position on every update. The impact is minor.

These are sample logs that show timestamps at beginning
and end of atomic_check, commit_tail, handle_cursor_update,
and before and after cursor_attribute and cursor_position
calls:

[   66.800353] hwhw: begin of check
[   66.800377] hwhw: end of check
[   66.800428] hwhw: begin of commit_tail
[   66.800441] hwhw: begin of cursor
[   66.800449] hwhw: begin of cursor_attr
[   66.800468] hwhw: end of cursor_attr
[   66.800484] hwhw: end of cursor_positionr
[   66.800501] hwhw: end of commit_tail
[   66.807139] hwhw: begin of check
[   66.807160] hwhw: end of check
[   66.807206] hwhw: begin of commit_tail
[   66.807217] hwhw: begin of cursor
[   66.807225] hwhw: begin of cursor_attr
[   66.807357] hwhw: end of cursor_attr
[   66.807374] hwhw: end of cursor_positionr
[   66.807392] hwhw: end of commit_tail

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>