proc: switch /proc/scsi/device_info to seq_file interface

Note 1: 0644 should be used, but root bypasses permissions, so writing
	to /proc/scsi/device_info still works.
Note 2: looks like scsi_dev_info_list is unprotected
Note 3: probably make proc whine about "unwriteable but with ->write hook"
	entries. Probably.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Cc: James Bottomley <James.Bottomley@SteelEye.com>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>