PCI/MSI: Add "msi_bus" sysfs MSI/MSI-X control for endpoints
The "msi_bus" sysfs file for bridges sets a bus flag to allow or disallow
future driver requests for MSI or MSI-X. Previously, the sysfs file
existed for endpoints but did nothing.
Add "msi_bus" support for endpoints, so an administrator can prevent the
use of MSI and MSI-X for individual devices.
Note that as for bridges, these changes only affect future driver requests
for MSI or MSI-X, so drivers may need to be reloaded.