ppc: Mark the 'taihu' machine as deprecated

ppc: Mark the 'taihu' machine as deprecated

The PPC 405 CPU is a system-on-a-chip, so all 405 machines are very similar,
except for some external periphery. However, the periphery of the 'taihu'
machine is hardly emulated at all (e.g. neither the LCD nor the USB part had
been implemented), so there is not much value added by this board. The users
can use the 'ref405ep' machine to test their PPC405 code instead.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20211203164904.290954-2-thuth@redhat.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20211206103712.1866296-3-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>