[PATCH] libata: update ata_host_init() and rename it to ata_port_init_shost()

Update ata_host_init() such that it only initializes SCSI host related
stuff and doesn't call into ata_port_init(), and rename it to
ata_port_init_shost().

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