drm/amd: Use attribute groups for PSP flashing attributes

Individually creating attributes can be racy, instead make attributes
using attribute groups and control their visibility with an is_visible
callback to only show when using appropriate products.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>