Kernel/PCI: Don't use x86 initialization methods in non-x86 builds

Using the IO address space is only relevant for x86 machines, so let's
not compile instructions to access the PCI configuration space when we
don't target x86 platforms.

Kernel/Bus/PCI/Initializer.cpp

@@ -23,6 +23,7 @@ static bool test_pci_io();
 
 UNMAP_AFTER_INIT static PCIAccessLevel detect_optimal_access_type()
 {
+#if ARCH(I386) || ARCH(X86_64)
     auto boot_determined = kernel_command_line().pci_access_level();
     if (!ACPI::is_enabled() || !ACPI::Parser::the()->find_table("MCFG"sv).has_value())
         return PCIAccessLevel::IOAddressing;
@@ -32,6 +33,7 @@ UNMAP_AFTER_INIT static PCIAccessLevel detect_optimal_access_type()
 
     if (!g_pci_access_io_probe_failed)
         return PCIAccessLevel::IOAddressing;
+#endif
 
     PANIC("No PCI bus access method detected!");
 }
@@ -44,17 +46,21 @@ UNMAP_AFTER_INIT void initialize()
         return;
     switch (detect_optimal_access_type()) {
     case PCIAccessLevel::MemoryAddressing: {
+        // FIXME: There are other arch-specific methods to find the memory range
+        // for accessing the PCI configuration space.
         auto mcfg = ACPI::Parser::the()->find_table("MCFG"sv);
         VERIFY(mcfg.has_value());
         auto success = Access::initialize_for_multiple_pci_domains(mcfg.value());
         VERIFY(success);
         break;
     }
+#if ARCH(I386) || ARCH(X86_64)
     case PCIAccessLevel::IOAddressing: {
         auto success = Access::initialize_for_one_pci_domain();
         VERIFY(success);
         break;
     }
+#endif
     default:
         VERIFY_NOT_REACHED();
     }

Kernel/CommandLine.cpp

@@ -149,8 +149,10 @@ UNMAP_AFTER_INIT PCIAccessLevel CommandLine::pci_access_level() const
     auto value = lookup("pci"sv).value_or("ecam"sv);
     if (value == "ecam"sv)
         return PCIAccessLevel::MemoryAddressing;
+#if ARCH(I386) || ARCH(X86_64)
     if (value == "io"sv)
         return PCIAccessLevel::IOAddressing;
+#endif
     if (value == "none"sv)
         return PCIAccessLevel::None;
     PANIC("Unknown PCI ECAM setting: {}", value);

Kernel/CommandLine.h

@@ -32,7 +32,9 @@ enum class AcpiFeatureLevel {
 
 enum class PCIAccessLevel {
     None,
+#if ARCH(I386) || ARCH(X86_64)
     IOAddressing,
+#endif
     MemoryAddressing,
 };