add helpers to dump max inflight io time for one disk and its disk driver

[biger410]

Two columns "DRIVER" and "Max Inflight time" are added.

>>> from drgn_tools import blockinfo
>>> blockinfo.print_block_devs_info(prog)
MAJOR  GENDISK             NAME   DRIVER       REQUEST_QUEUE       Inflight I/Os  Max Inflight time  Freezed Depth  Usage Counter
8      0xffff99155b391a00  sda    virtio_scsi  0xffff99154b323990  0              0 00:00:00.000     0              1
252    0xffff99154105c000  dm-0   linear       0xffff99154b321cc8  0              0 00:00:00.000     0              1
252    0xffff9915425e2200  dm-1   linear       0xffff9915c967d658  0              0 00:00:00.000     0              1
8      0xffff9915428ad800  sdb    iscsi_tcp    0xffff99154b320998  0              0 00:00:00.000     0              1
8      0xffff991547dfe800  sdc    iscsi_tcp    0xffff99154b320000  24             0 00:00:00.418     0              30
7      0xffff9915c95ba000  loop0  loop         0xffff9915c96d2ff8  110            0 00:00:16.316     0              111
9      0xffff991547e46c00  md0    raid456      0xffff9915c967dff0  0              0 00:00:00.000     0              4
7      0xffff99154611b200  loop1  loop         0xffff9915c96d0998  48             0 00:00:03.658     0              49
7      0xffff991558d6f000  loop2  loop         0xffff9915c967f320  123            0 00:00:09.403     0              125
7      0xffff9915428acc00  loop3  loop         0xffff9915c96d4328  12             0 00:00:03.990     0              13
7      0xffff99154089d400  loop4  loop         0xffff9915c96d0000  32             0 00:00:02.074     0              33
7      0xffff991542f5d400  loop5  loop         0xffff99154b322660  34             0 00:00:32.587     0              38
7      0xffff991548970000  loop6  loop         0xffff9915c96d1330  118            0 00:00:31.792     0              119
7      0xffff9915594d5200  loop7  loop         0xffff9915c9679330  128            0 00:00:36.261     0              131
9      0xffff9915494cf400  md1    raid1        0xffff991592393990  0              0 00:00:00.000     0              1
9      0xffff99154ab67400  md2    raid0        0xffff991592391330  0              0 00:00:00.000     0              1
>>>