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/am57xx_hs_evm_usb_defconfig b/configs/am57xx_hs_evm_usb_defconfig
index 7f19d99..10106ab 100644
--- a/configs/am57xx_hs_evm_usb_defconfig
+++ b/configs/am57xx_hs_evm_usb_defconfig
@@ -102,6 +102,7 @@
 CONFIG_PMIC_PALMAS=y
 CONFIG_DM_REGULATOR=y
 CONFIG_DM_REGULATOR_PALMAS=y
+CONFIG_SCSI_AHCI_PLAT=y
 CONFIG_DM_SERIAL=y
 CONFIG_SPI=y
 CONFIG_DM_SPI=y