tty/vt: consolemap: improve UNI_*() macros definitions

tty/vt: consolemap: improve UNI_*() macros definitions

Use FIELD_GET() and GENMASK() helpers instead of direct shifts and ANDs.
This makes the code even more obvious. I didn't know about the helpers
at the time of writing the macros.

Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220614090537.15557-6-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>