!1202 [sync] PR-1148: LoongArch: cleanup swiotlb bakcup buffer related code

Merge Pull Request from: @openeuler-sync-bot 
 

Origin pull request: 
https://gitee.com/openeuler/kernel/pulls/1148 
 
cleanup swiotlb bakcup buffer related code,not used now. 
 
Link:https://gitee.com/openeuler/kernel/pulls/1202 

Reviewed-by: Jialin Zhang <zhangjialin11@huawei.com> 
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com> 

arch/loongarch/Kconfig

@@ -113,8 +113,6 @@ config LOONGARCH
 	select MODULES_USE_ELF_RELA if MODULES
 	select NEED_PER_CPU_EMBED_FIRST_CHUNK
 	select NEED_PER_CPU_PAGE_FIRST_CHUNK
-	select DMA_OPS
-	select ARCH_HAS_SETUP_DMA_OPS
 	select OF
 	select OF_EARLY_FLATTREE
 	select PCI

arch/loongarch/include/asm/dma-mapping.h

-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * Copyright (C) 2020 Loongson Technology Corporation Limited
- */
-#ifndef _ASM_DMA_MAPPING_H
-#define _ASM_DMA_MAPPING_H
-
-extern const struct dma_map_ops loongson_dma_ops;
-extern bool swiotlb_need_fix;
-extern phys_addr_t io_tlb_start;
-
-static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
-{
-	if (swiotlb_need_fix)
-		return &loongson_dma_ops;
-	else
-		return NULL;
-}
-
-#endif /* _ASM_DMA_MAPPING_H */