[PATCH] SCSI_SATA has to be a tristate

SCSI=m must disallow static drivers.

The problem is that all the SATA drivers depend on SCSI_SATA.

With SCSI=m and SCSI_SATA=y this allows the static enabling of the SATA
drivers with unwanted effects, e.g.:
- SCSI=m, SCSI_SATA=y, SCSI_ATA_ADMA=y
  -> SCSI_ATA_ADMA is built statically but scsi/built-in.o is not linked
     into the kernel
- SCSI=m, SCSI_SATA=y, SCSI_ATA_ADMA=y, SCSI_SATA_AHCI=m
  -> SCSI_ATA_ADMA and libata are built statically but
     scsi/built-in.o is not linked into the kernel,
     SCSI_SATA_AHCI is built modular (unresolved symbols due to missing
                                      libata)

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Cc: Jeff Garzik <jgarzik@pobox.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>