KVM: x86: Isolate edge vs. level check in userspace I/O APIC route scanning

Extract and isolate the trigger mode check in kvm_scan_ioapic_routes() in
anticipation of moving destination matching logic to a common helper (for
userspace vs. in-kernel I/O APIC emulation).

No functional change intended.

Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20250304013335.4155703-2-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>