vmm: Remove PCI PIO optimisation

This optimisation provided some peformance improvement when measured by
perf however when considered in terms of boot time peformance this
optimisation doesn't have any impact measurable using our
peformance-metrics tooling.

Removing this optimisation helps simplify the VMM internals as it allows
the reordering of the VM creation process permitting refactoring of the
restore code path.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/device_manager.rs

@@ -54,8 +54,6 @@ use libc::{
     cfmakeraw, isatty, tcgetattr, tcsetattr, termios, MAP_NORESERVE, MAP_PRIVATE, MAP_SHARED,
     O_TMPFILE, PROT_READ, PROT_WRITE, TCSANOW,
 };
-#[cfg(target_arch = "x86_64")]
-use pci::PciConfigIo;
 use pci::{
     DeviceRelocation, PciBarRegionType, PciBdf, PciDevice, VfioPciDevice, VfioUserDmaMapping,
     VfioUserPciDevice, VfioUserPciDeviceError,
@@ -3564,12 +3562,6 @@ impl DeviceManager {
             .map(|ic| ic.clone() as Arc<Mutex<dyn InterruptController>>)
     }
 
-    #[cfg(target_arch = "x86_64")]
-    // Used to provide a fast path for handling PIO exits
-    pub fn pci_config_io(&self) -> Arc<Mutex<PciConfigIo>> {
-        Arc::clone(self.pci_segments[0].pci_config_io.as_ref().unwrap())
-    }
-
     pub(crate) fn pci_segments(&self) -> &Vec<PciSegment> {
         &self.pci_segments
     }