venus: fix bo_flags and workaround a mmap_size issue for AHB
1st commit renames dmabuf
to dma_buf
2nd commit fixes a bo_flags mismatch issue between the pure import and the later fd props query
3rd commit refactors the logic to retrieve size and mem type bits from a dma_buf fd
4th commit fixes a bug that mmap_size
increases between the initial allocation and later import for AHB
Test: dEQP-VK.api.*
(including AHB) and dEQP-VK.memory.*
/cc @olv