nvme: do not touch INTMS/INTMC when configured for MSI-X

The single-vector MSI-X fallback installs the shared interrupt
handler, which masks interrupts through INTMS/INTMC around the
completion poll.
INTx and MSI are unaffected. Only MSI-X track the interrupt mode
and skip un/masking

Reviewed by:	ngie, imp, adrian
Differential Revision:	https://reviews.freebsd.org/D59637

sys/dev/nvme/nvme_ctrlr.c

@@ -1405,9 +1405,12 @@ nvme_ctrlr_shared_handler(void *arg)
 {
 	struct nvme_controller *ctrlr = arg;
 
-	nvme_mmio_write_4(ctrlr, intms, 1);
+	/* INTMS/INTMC are undefined when configured for MSI-X. */
+	if (!ctrlr->is_msix)
+		nvme_mmio_write_4(ctrlr, intms, 1);
 	nvme_ctrlr_poll(ctrlr);
-	nvme_mmio_write_4(ctrlr, intmc, 1);
+	if (!ctrlr->is_msix)
+		nvme_mmio_write_4(ctrlr, intmc, 1);
 }
 
 #define NVME_MAX_PAGES  (int)(1024 / sizeof(vm_page_t))

sys/dev/nvme/nvme_pci.c

@@ -385,6 +385,7 @@ again:
 		ctrlr->msi_count = 0;
 		goto msi;
 	}
+	ctrlr->is_msix = true;
 	if (ctrlr->msi_count == 1)
 		return (nvme_ctrlr_setup_shared(ctrlr, 1));
 	if (ctrlr->msi_count != num_vectors_requested) {

sys/dev/nvme/nvme_private.h

@@ -257,6 +257,7 @@ struct nvme_controller {
 	struct resource		*msix_pba_resource;
 
 	int			msi_count;
+	bool			is_msix;
 	uint32_t		enable_aborts;
 
 	uint32_t		num_io_queues;