Revert "MIPS: SiByte: Enable swiotlb for SWARM, LittleSur and BigSur"

This reverts commit c85acbf7 which is
commit e4849aff upstream

Guenter writes:
	Upstream commit e4849aff

 ("MIPS: SiByte: Enable swiotlb for SWARM,
	LittleSur and BigSur") results in build failures in v4.4.y and v4.14.y.

	make bigsur_defconfig:

	warning: (SIBYTE_SWARM && SIBYTE_SENTOSA && SIBYTE_BIGSUR && SWIOTLB_XEN && AMD_IOMMU) selects SWIOTLB which has unmet direct dependencies (CAVIUM_OCTEON_SOC || MACH_LOONGSON64 && CPU_LOONGSON3 || NLM_XLP_BOARD || NLM_XLR_BOARD)
	warning: (SIBYTE_SWARM && SIBYTE_SENTOSA && SIBYTE_BIGSUR && SWIOTLB_XEN && AMD_IOMMU) selects SWIOTLB which has unmet direct dependencies (CAVIUM_OCTEON_SOC || MACH_LOONGSON64 && CPU_LOONGSON3 || NLM_XLP_BOARD || NLM_XLR_BOARD)

	and the actual build:

	lib/swiotlb.o: In function `swiotlb_tbl_map_single':
	(.text+0x1c0): undefined reference to `iommu_is_span_boundary'
	Makefile:1021: recipe for target 'vmlinux' failed

Reported-by: Guenter Roeck <linux@roeck-us.net>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>