drm/amdkfd: Use bitmap_zalloc() when applicable

'kfd->gtt_sa_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>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -873,8 +873,6 @@ int kgd2kfd_schedule_evict_and_restore_process(struct mm_struct *mm,
 static int kfd_gtt_sa_init(struct kfd_dev *kfd, unsigned int buf_size,
 				unsigned int chunk_size)
 {
-	unsigned int num_of_longs;
-
 	if (WARN_ON(buf_size < chunk_size))
 		return -EINVAL;
 	if (WARN_ON(buf_size == 0))
@@ -885,11 +883,8 @@ static int kfd_gtt_sa_init(struct kfd_dev *kfd, unsigned int buf_size,
 	kfd->gtt_sa_chunk_size = chunk_size;
 	kfd->gtt_sa_num_of_chunks = buf_size / chunk_size;
 
-	num_of_longs = (kfd->gtt_sa_num_of_chunks + BITS_PER_LONG - 1) /
-		BITS_PER_LONG;
-
-	kfd->gtt_sa_bitmap = kcalloc(num_of_longs, sizeof(long), GFP_KERNEL);
-
+	kfd->gtt_sa_bitmap = bitmap_zalloc(kfd->gtt_sa_num_of_chunks,
+					   GFP_KERNEL);
 	if (!kfd->gtt_sa_bitmap)
 		return -ENOMEM;
 
@@ -899,13 +894,12 @@ static int kfd_gtt_sa_init(struct kfd_dev *kfd, unsigned int buf_size,
 	mutex_init(&kfd->gtt_sa_lock);
 
 	return 0;
-
 }
 
 static void kfd_gtt_sa_fini(struct kfd_dev *kfd)
 {
 	mutex_destroy(&kfd->gtt_sa_lock);
-	kfree(kfd->gtt_sa_bitmap);
+	bitmap_free(kfd->gtt_sa_bitmap);
 }
 
 static inline uint64_t kfd_gtt_sa_calc_gpu_addr(uint64_t start_addr,