vga-switcheroo with apple-gmux does not switch correctly on my system. The PCI
configuration space is not restored correctly, resulting in MSI not working after switch.

Only useful item in dmesg is:

[   33.922807] radeon 0000:01:00.0: Refused to change power state, currently in D3

I did some testing, dumping the difference in ms between first succesful switch
from D3 to D0, and it seems that there is slightly more than 20 ms difference when
the device is re-enabled through vga-switcheroo.

So bump the re-enable d3 delay to 20 ms to handle this, which fixes msi not working
on my system after switcheroo-ing. Default d3_delay value is PCI_PM_D3_WAIT, 10 ms.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>