f2fs: use iostat_lat_type directly as a parameter in the iostat_update_and_unbind_ctx()

Convert to use iostat_lat_type as parameter instead of raw number.
BTW, move NUM_PREALLOC_IOSTAT_CTXS to the header file, adjust
iostat_lat[{0,1,2}] to iostat_lat[{READ_IO,WRITE_SYNC_IO,WRITE_ASYNC_IO}]
in tracepoint function, and rename iotype to page_type to match the definition.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>