nyan-big: drop CONFIG_KEYBOARD

The CONFIG_KEYBOARD does nothing as it's legacy and unused
so just drop it from the config.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Cc: Tom Warren <twarren@nvidia.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Allen Martin <amartin@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>