drm/amd/display: Fix idle optimization checks for multi-display and dual eDP

[Why]
Idle optimizations are blocked if there's more than one eDP connector
on the board - blocking S0i3 and IPS2 for static screen.

[How]
Fix the checks to correctly detect number of active eDP.
Also restrict the eDP support to panels that have correct feature
support.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>