FRV: Be (self-)consistent and use CONFIG_GDB_CONSOLE everywhere

Be (self-)consistent and use CONFIG_GDB_CONSOLE everywhere rather than using
CONFIG_GDBSTUB_CONSOLE in some places and not others.  This is also then
consistent with other archs.

Also remove the gdbstub console device() op which doesn't seem to be necessary
now (especially as it doesn't compile).

[Found by Robert P. J. Day <rpjday@mindspring.com>]

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>