lenovo/t60: Enable dock serial port when undocked and redocked

When the system is started with dock, the serial port works.
As soon as the laptop is undocked and redocked, the serial port
no longer works.  See below superiotool dump snippet:

Upon bootup: SIO @ 0x2e
LDN 0x03 (COM1)
idx 30 60 61 70 71 74 75 f0
val 01 03 f8 04 03 04 04 02

Redocked:    SIO @ 0x2e
LDN 0x03 (COM1)
idx 30 60 61 70 71 74 75 f0
val 00 03 f8 04 03 04 04 02

Since the function dock_connect is executed every time the
dock is reconnected, starting without a dock and then attaching
it to a dock is now also fixed.

Change-Id: Ibd97589a8c743673a55e382a5db2ba62656c595e
Signed-off-by: Damien Zammit <damien@zamaudio.com>
Reviewed-on: http://review.coreboot.org/5761
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>