Bring back console_start_log_everything() as a milder alternative to

Bring back console_start_log_everything() as a milder alternative to
console_start_sync(). Revert keyhandler logic to use it. The
difference now is that serial logic is updated to not drop characters
if inb a log_everything region. Still this is milder than a sync
region since the async buffer must be filled before we start to
busy-wait on each character.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>