ahci_init_controller() calls ahci_deinit_port() to make sure the
controller is stopped before initializing the controller.  In turn,
ahci_deinit_port() invokes ahci_power_down() to power down the port.
If the controller supports slumber mode, the link is put into it.

Unfortunately, some devices don't implement link powersaving mode
properly and show erratic behavior after link is put into slumber
mode.  For example, HL-DT-ST DVD-RAM GSA-H30N completely locks up on
slumber transition and can only be recovered with the *REAL* hard
reset - power removal and reapply.

Note that this makes the first probing reset different from all
others.  If the above dvd-ram is hotplugged after ahci is initialized,
no problem occurs because ahci is already fully initialized with phy
powered up.  So, this might also be the reason for other weird AHCI
initial probing abnormalities.

This patch moves power up/down out of port init/deinit and call them
only when needed.

Power down is now called only when suspending.  As system suspend
usually involves powering down 12v for storage devices, this shouldn't
cause problem even if the attached device doesn't support slumber
mode.  However, in partial power management and suspend failure cases,
devices might lock up after suspend attempt.  I thought about removing
transition to slumber mode altogether but ahci spec mandates it before
HBA D3 state transition.  Blacklisting such devices might be the
solution.

Signed-off-by: Tejun Heo <htejun@gmail.com>