anv: always annotate memory returned from anv_gem_mmap
anv_bo_pool_alloc expects that the memory returned by and_gem_mmap was annotated using VALGRIND_MALLOCLIKE_BLOCK, but anv_gem_mmap_offset didn't do that. Move annotation from anv_gem_mmap_legacy to common code.
Fixes: 4abf0837 ("anv: Add support for new MMAP_OFFSET ioctl.")