Add 3wire and std as terminal types/classes. These are similar to

the existing terminal types/classes that have the baudrate suffix,
but differ in that no baudrate is set/defined.

The purpose of these new types/classes is to allow them to be used
for the serial console. Currently the uart(4) driver fixates the
baudrate and the CLOCAL flag, which means that it doesn't matter
whether you give it std.<baud> or 3wire.<baud> as the terminal type
to getty and what exactly <baud> is set to. It's being overridden
by uart(4). The goal is to change uart(4) not to override these
settings.

etc/gettytab

@@ -49,6 +49,8 @@ default:\
 #	autobaud code in getty, and likewise can
 #	be assigned to any table desired (hopefully the same speed).
 #
+std:\
+	:np:sp#0:
 a|std.110|110-baud:\
 	:np:nd#1:cd#1:uc:sp#110:
 b|std.134|134.5-baud:\
@@ -221,6 +223,8 @@ al.Pc:\
 # Entries for 3-wire serial terminals.  These don't supply carrier, so
 # clocal needs to be set, and crtscts needs to be unset.
 #
+3wire:\
+	:np:nc:sp#0:
 3wire.9600|9600-3wire:\
 	:np:nc:sp#9600:
 3wire.19200|19200-3wire:\