9pfs: performance fix and cleanup
* First patch fixes suboptimal I/O performance on guest due to previously
incorrect block size being transmitted to 9p client.
* Subsequent patches are cleanup ones intended to reduce code complexity.
* remotes/cschoenebeck/tags/pull-9p-
20211027:
9pfs: use P9Array in v9fs_walk()
9pfs: make V9fsPath usable via P9Array API
9pfs: make V9fsString usable via P9Array API
fsdev/p9array.h: check scalar type in P9ARRAY_NEW()
9pfs: introduce P9Array
9pfs: simplify blksize_to_iounit()
9pfs: deduplicate iounit code
9pfs: fix wrong I/O block size in Rgetattr
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>