device: dumpstate: expand f2fs dump script

With the recent changes in partition mapping, multiple f2fs partitions
exists and is not fixed to specific dm-x. To address this, update the
script to dynamically locate f2fs partitions.

New log:
------ F2FS - fragmentation (/vendor/bin/sh -c for d in $(ls /proc/fs/f2fs/); ...
dm-4: /dev/block/mapper/scratch -> /dev/block/dm-4
format: segment_type|valid_blocks
segment_type(0:HD, 1:WD, 2:CD, 3:HN, 4:WN, 5:CN)
0         3|18  4|2   5|0   0|1   0|0   0|0   0|0   0|0   0|0   0|0
10        0|0   0|0   0|0   0|0   0|0   0|0   0|0   0|0   0|0   0|0
...
dm-5: /dev/block/mapper/userdata -> /dev/block/dm-5
format: segment_type|valid_blocks
segment_type(0:HD, 1:WD, 2:CD, 3:HN, 4:WN, 5:CN)
0         3|330 0|147 5|5   0|68  0|32  0|77  4|112 3|13  0|42  0|75
10        4|30  3|69  0|98  0|45  0|56  0|128 0|185 0|36  0|104 3|84
...

Bug: 137150088
Test: run bugreport and check f2fs dump
Change-Id: I5546f35f543628282a58dae38a72a379d5e56b0b
Signed-off-by: Leo Liou <leoliou@google.com>