dev: Add a dummy serial device

Add a dummy serial device that discards any output and doesn't provide
any input. This device can be used to terminate UARTs that don't have
a default device (e.g., a terminal) attached.

Change-Id: I4a6b0b5037ce360f59bfb5c566e1698d113a1d26
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/4290
Reviewed-by: Gabe Black <gabeblack@google.com>
3 files changed