vmm: exclude legacy serial port I/O ranges from PCI Root Complex _CRS

The PCI Root Complex ACPI _CRS (Current Resource Settings) was claiming
the entire legacy I/O range 0x000-0xCF7, which includes the COM1-COM4
serial port addresses. This causes a resource conflict on Windows guests
where Windows Device Manager shows:

  ACPI\PNP0501\0 - COM1, Problem Code 12 (CM_PROB_NORMAL_CONFLICT)

Windows refuses to load drivers for devices when their I/O resources
overlap with another device's claimed range. The serial port driver
fails to load because the PCI Root Complex already claims 0x3F8-0x3FF.

This patch splits the I/O range to exclude the legacy COM port addresses:
- 0x000-0x2E7 (before COM4)
- 0x400-0xCF7 (after COM1)

The excluded range 0x2E8-0x3FF covers all four standard COM ports:
- COM1: 0x3F8-0x3FF
- COM2: 0x2F8-0x2FF
- COM3: 0x3E8-0x3EF
- COM4: 0x2E8-0x2EF

This has no impact on Linux guests (which don't enforce strict ACPI
resource checking) or on modern PCI devices (which use MMIO BARs rather
than legacy I/O ports).

Signed-off-by: Taha Saifuddin <taha@blacksmith.sh>

Author: taha-au

vmm/src/pci_segment.rs

@@ -403,7 +403,15 @@ impl Aml for PciSegment {
                         None,
                     ),
                     #[cfg(target_arch = "x86_64")]
-                    &aml::AddressSpace::new_io(0u16, 0x0cf7u16, None),
+                    // Legacy I/O port ranges for PCI devices.
+                    // Excludes 0x2E8-0x3FF to avoid ACPI resource conflict with legacy serial
+                    // ports (COM1-COM4) on Windows. Windows refuses to load drivers for devices
+                    // when their I/O resources overlap with another device's claimed range.
+                    // COM ports: COM1=0x3F8, COM2=0x2F8, COM3=0x3E8, COM4=0x2E8 (each uses 8 bytes)
+                    #[cfg(target_arch = "x86_64")]
+                    &aml::AddressSpace::new_io(0x0000u16, 0x02e7u16, None),
+                    #[cfg(target_arch = "x86_64")]
+                    &aml::AddressSpace::new_io(0x0400u16, 0x0cf7u16, None),
                     #[cfg(target_arch = "x86_64")]
                     &aml::AddressSpace::new_io(0x0d00u16, 0xffffu16, None),
                 ]),