[PATCH v6] modify the IO_TLB_SEGSIZE and IO_TLB_DEFAULT_SIZE configurable as flexible requirement about SW-IOMMU.

The maximum of SW-IOMMU is limited to 2^11*128 = 256K. And the size of IO_TLB_DEFAULT_SIZE is limited to (64UL<<20) 64M now. While in different platform and different requirement this seems improper. So modifing the IO_TLB_SEGSIZE to io_tlb_segsize and IO_TLB_DEFAULT_SIZE to io_tlb_default_size

[PATCH v6] modify the IO_TLB_SEGSIZE and IO_TLB_DEFAULT_SIZE configurable as flexible requirement about SW-IOMMU.

The maximum of SW-IOMMU is limited to 2^11*128 = 256K. And the size of IO_TLB_DEFAULT_SIZE is limited to (64UL20) 64M now. While in different platform and different requirement this seems improper. So modifing the IO_TLB_SEGSIZE to io_tlb_segsize and IO_TLB_DEFAULT_SIZE to io_tlb_default_size