Kernel 2.6.35 (may be, earlier) split ahci into libahci.ko and ahci.ko
and added ahci_platform.ko. As a result, drivers ahci and ahci_platform
do not contain any symbol that are checked for storage modules (it is
libahci.ko that references ata_scsi_ioctl now). So add additional
symbol ahci_init_controller; it seems this is expected to be called by
every driver based on libahci.ko.
Signed-off-by: Andrey Borzenkov <arvidjaar@mail.ru>