tzdata: install /etc/localtime alongside /etc/timezone

tzdata: install /etc/localtime alongside /etc/timezone

Lots of code (such a GLib) expects this to exist and link to the current
timezone definition.

/etc/localtime is a symlink instead of a copy of hard link to make it obvious
what timezone data it's pointing at. For systems with /etc on a separate
filesystem to /usr this will result in a dangling symlink until /usr is mounted,
but as this is early boot the assumption is that anything checking it will
handle that case and fallback to UTC.

(From OE-Core rev: efe305c275f288e248655f3a8b266f86c9893f73)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>