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/configs/sandbox_spl_defconfig b/configs/sandbox_spl_defconfig
index 926c34c..cd1ad38 100644
--- a/configs/sandbox_spl_defconfig
+++ b/configs/sandbox_spl_defconfig
@@ -110,6 +110,7 @@
 # CONFIG_SPL_SIMPLE_BUS is not set
 CONFIG_ADC=y
 CONFIG_ADC_SANDBOX=y
+CONFIG_SYS_SATA_MAX_DEVICE=2
 CONFIG_AXI=y
 CONFIG_AXI_SANDBOX=y
 CONFIG_SYS_IDE_MAXBUS=1