vconsole-setup: enable utf-8 mode explicitly

vconsole-setup: enable utf-8 mode explicitly

Rather than assuming the console is in utf-8 mode if nothing else is
specified, be a bit more robust and enable it explicitly.

This fixes a regression compared with Arch's initscripts when not
using a framebuffer as the old VGA console would not be in utf-8
mode by default.

Furthermore, this would allow vconsole-setup to be used after boot
to change the vconsole into utf-8 mode in case it has been set to
non-utf-8 mode for whatever reason. I.e, the following would leave
the console in utf-8 mode as expected:

 # export LANG=en_US.ISO-8859-1
 # /usr/lib/systemd/systemd-vconsole-setup
 # export LANG=en_US.UTF-8
 # /usr/lib/systemd/systemd-vconsole-setup

Reported-by: Xyne <xyne@archlinx.ca>
Reported-by: Thomas Bächler <thomas@archlinux.org>
Cc: Dave Reisner <dreisner@archlinux.org>