drm/amd/pm: Fix incorrect comment about Vangogh power cap support

The comment mentions that power1 cap attributes are not supported on
Vangogh, but the opposite is indeed valid: for APUs, only Vangogh is
supported. While at it, also fixed the Renoir comment below (thanks
Melissa for noticing that!).

Cc: Lijo Lazar <lijo.lazar@amd.com>
Cc: Melissa Wen <mwen@igalia.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>