wifi: iwlwifi: limit EHT capabilities based on PCIe link speed

wifi: iwlwifi: limit EHT capabilities based on PCIe link speed

If a discrete NIC is connected to a PCIe link hat isn't at least
Gen3 (8.0 GT/s), then we cannot sustain 320 MHz traffic, so remove
that from EHT capabilities in that case.

While at it, also move setting 320 MHz beamformee to the right
place in the code so it's not set while not supporting 320 MHz.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230620125813.b77a1574a0a7.Id4120c161fb7df6dedc70d5f3e3829e9117b8cb1@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>