Convert CONFIG_SCSI_AHCI_PLAT et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SCSI_AHCI_PLAT
   CONFIG_SYS_SCSI_MAX_SCSI_ID
   CONFIG_SYS_SCSI_MAX_LUN
   CONFIG_SYS_SATA_MAX_DEVICE

Drop CONFIG_SCSI for everything except the sandbox build. We only need
one build for tests.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/scsi/Makefile b/drivers/scsi/Makefile
index e9f8486..25194ee 100644
--- a/drivers/scsi/Makefile
+++ b/drivers/scsi/Makefile
@@ -15,4 +15,6 @@
 endif
 endif
 
+ifdef CONFIG_SCSI
 obj-$(CONFIG_SANDBOX) += sandbox_scsi.o
+endif