liblp: change some functions to use string_view

Converting all of them to string_view requires some
non-trivial amount of refactoring (because there is not
an implicit conversion from string_view to string), and
hence may be done later if necessary.

Test: builds
Bug: 135752105
Change-Id: I936ae7117500fadc7b34a5b91b279bc863d9919d
2 files changed