vt: switch G0/1_charset to an array

Declare Gx_charset[2] instead of G0_charset and G1_charset. It makes
the code simpler (without ternary operators).

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200615074910.19267-5-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>