drm/amdkfd: Use bitmap_zalloc() when applicable

'doorbell_bitmap' is a bitmap. So use 'bitmap_zalloc()' to simplify code,
improve the semantic and avoid some open-coded arithmetic in allocator
arguments.

Also change the corresponding 'kfree()' into 'bitmap_free()' to keep
consistency.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

drivers/gpu/drm/amd/amdkfd/kfd_process.c

@@ -1011,7 +1011,7 @@ static void kfd_process_destroy_pdds(struct kfd_process *p)
 			free_pages((unsigned long)pdd->qpd.cwsr_kaddr,
 				get_order(KFD_CWSR_TBA_TMA_SIZE));
 
-		kfree(pdd->qpd.doorbell_bitmap);
+		bitmap_free(pdd->qpd.doorbell_bitmap);
 		idr_destroy(&pdd->alloc_idr);
 
 		kfd_free_process_doorbells(pdd->dev, pdd->doorbell_index);
@@ -1434,9 +1434,8 @@ static int init_doorbell_bitmap(struct qcm_process_device *qpd,
 	if (!KFD_IS_SOC15(dev->device_info->asic_family))
 		return 0;
 
-	qpd->doorbell_bitmap =
-		kzalloc(DIV_ROUND_UP(KFD_MAX_NUM_OF_QUEUES_PER_PROCESS,
-				     BITS_PER_BYTE), GFP_KERNEL);
+	qpd->doorbell_bitmap = bitmap_zalloc(KFD_MAX_NUM_OF_QUEUES_PER_PROCESS
+					     GFP_KERNEL);
 	if (!qpd->doorbell_bitmap)
 		return -ENOMEM;