mb/google/skyrim: Re-enable hotplug for SD

It seems like the hotplug enable might be doing more than just enabling
devices to be hot-plugged, so re-enable the feature for the SD card.
Removing it from SD increased resume time and may have caused reboot
issues for SD after resume.

This is a partial revert of CB:73512

BUG=b:273620322
TEST=See resume time go down on Skyrim
BRANCH=Skyrim

Change-Id: I4814d4377d0ba8a1e9b308853b3e02a4a27bd8d5
Signed-off-by: Martin Roth <gaumless@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73868
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Frank Wu <frank_wu@compal.corp-partner.google.com>
Reviewed-by: John Su <john_su@compal.corp-partner.google.com>
Reviewed-by: Jon Murphy <jpmurphy@google.com>

src/mainboard/google/skyrim/port_descriptors.c

@@ -32,6 +32,7 @@ static const fsp_dxio_descriptor skyrim_mdn_dxio_descriptors[] = {
 		.function_number = PCI_FUNC(SD_DEVFN),
 		.link_speed_capability = GEN3,
 		.turn_off_unused_lanes = true,
+		.link_hotplug = 3,
 		.link_aspm = ASPM_L1,
 		.link_aspm_L1_1 = true,
 		.link_aspm_L1_2 = true,