libata: ahci enclosure management bios workaround

During driver initialization ahci_start_port may not be able
to turn LEDs off because the hardware may still be transmitting
a message. And since the BIOS may not be setting the LEDs to
off the drive LEDs may end up in a fault state. This has
been seen on ICH9r and ICH10r when configured in AHCI mode
instead of RAID mode, this patch doesn't key off a specific
set of device IDs but will give the EM transmit bit a chance
to clear if busy.

Signed-off-by: David Milburn <dmilburn@redhat.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>