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/pg_wcom_seli8_defconfig b/configs/pg_wcom_seli8_defconfig
index 229535c..f9bd076 100644
--- a/configs/pg_wcom_seli8_defconfig
+++ b/configs/pg_wcom_seli8_defconfig
@@ -79,6 +79,7 @@
 CONFIG_MII=y
 CONFIG_TSEC_ENET=y
 CONFIG_SYS_QE_FW_ADDR=0x60020000
+CONFIG_SCSI_AHCI_PLAT=y
 CONFIG_SPECIFY_CONSOLE_INDEX=y
 CONFIG_DM_SERIAL=y
 CONFIG_SYS_NS16550=y