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/ls1021atsn_sdcard_defconfig b/configs/ls1021atsn_sdcard_defconfig
index a3b8f24..627038c 100644
--- a/configs/ls1021atsn_sdcard_defconfig
+++ b/configs/ls1021atsn_sdcard_defconfig
@@ -78,6 +78,7 @@
 CONFIG_NVME=y
 CONFIG_PCI=y
 CONFIG_PCIE_LAYERSCAPE_RC=y
+CONFIG_SCSI_AHCI_PLAT=y
 CONFIG_SYS_NS16550=y
 CONFIG_SPI=y
 CONFIG_DM_SPI=y