firmware: ibft depends on SCSI

Prevent build errors when SCSI is not enabled:

iscsi_ibft.c:(.init.text+0x548d): undefined reference to `iscsi_boot_create_initiator'
iscsi_ibft.c:(.init.text+0x54a9): undefined reference to `iscsi_boot_create_ethernet'
iscsi_ibft.c:(.init.text+0x54c5): undefined reference to `iscsi_boot_create_target'
iscsi_ibft.c:(.init.text+0x55ff): undefined reference to `iscsi_boot_destroy_kset'
iscsi_ibft.c:(.init.text+0x561e): undefined reference to `iscsi_boot_create_kset'
iscsi_ibft.c:(.exit.text+0xe2c): undefined reference to `iscsi_boot_destroy_kset'

Signed-off-by: Randy Dunlap <[e-mail]>
Signed-off-by: Peter Jones <[e-mail]>
Signed-off-by: Konrad Rzeszutek Wilk <[e-mail]>

drivers/firmware/Kconfig

···
 config ISCSI_IBFT
 	tristate "iSCSI Boot Firmware Table Attributes module"
 	select ISCSI_BOOT_SYSFS
-	depends on ISCSI_IBFT_FIND
+	depends on ISCSI_IBFT_FIND && SCSI
 	default	n
 	help
 	  This option enables support for detection and exposing of iSCSI