linuxkpi: Add option to skip trailing newline in lkpi_hex_dump()

This will be useful in the upcoming implementation of
hex_dump_to_buffer() which doesn't add one.

Reviewed by: bz, emaste
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D51844

(cherry picked from commit 43b5a264c6f665ac451102d828a8f51307efe626)