esp: handle "select without attention"

esp: handle "select without attention"

Up to now "select without attention" was handled the same way as
"select with attention". According to

http://www.ibiblio.org/pub/historic-linux/early-ports/Sparc/NCR/NCR53C9X.txt

select without ATN sends the CDB (Command Descriptor Block) directly,
whereas select with ATN sends one message phase byte
followed by 6, 10, or 12 command phase bytes.

The attached patch implements the behaviour described above.

Signed-off-by: Artyom Tarasenko <atar4qemu@gmail.com>
[blauwirbel@gmail.com: cleaned up formatting]
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>