init: add a copy_per_line built-in command

There are sysfs nodes that don't take multiple inputs, adding a new
copy_per_line built-in command to copy from source file to destination
line by line.

Bug: 171740453
Test: boot and check file and log
Change-Id: I41b7a565829299d56b81d4509525dfa6a0a52444
2 files changed