LoongArch: Remove the unused dma-direct.h

dma-direct.h is introduced in commit d4b6f156 ("LoongArch: Add
Non-Uniform Memory Access (NUMA) support"). In commit c78c43fe
("LoongArch: Use acpi_arch_dma_setup() and remove ARCH_HAS_PHYS_TO_DMA"),
ARCH_HAS_PHYS_TO_DMA was deselected and the coresponding phys_to_dma()/
dma_to_phys() functions were removed. However, the unused dma-direct.h
was left behind, which is removed by this patch.

Cc: <stable@vger.kernel.org>
Fixes: c78c43fe

 ("LoongArch: Use acpi_arch_dma_setup() and remove ARCH_HAS_PHYS_TO_DMA")
Signed-off-by: Miao Wang <shankerwangmiao@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>