drm/amd/display: Update VCP X.Y logging to improve usefulness

[Why]
Recently debugging efforts have involved setting/checking the
X.Y value used during payload allocation. Current output for
Y was calculated with incorrect bitshift. Y value is also not
human readable.

[How]
Refactor logging into separate function. Fix Y calculation error
and format output to be human readable.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>