firmware: imx: fix compile-testing

It is nice to allow compile-testing the firmware drivers, but this
fails when the dependency is a loadable module:

aarch64-linux-ld: drivers/firmware/imx/scu-pd.o: in function `imx_sc_pd_power':
scu-pd.c:(.text+0xd8): undefined reference to `imx_scu_call_rpc'
aarch64-linux-ld: scu-pd.c:(.text+0x108): undefined reference to `imx_scu_call_rpc'
aarch64-linux-ld: drivers/firmware/imx/scu-pd.o: in function `imx_sc_pd_probe':

Change the dependencies to ensure that any driver we depend on is
either reachable or we are compile-testing and it is disabled,
effectively reverting most of the previous changes that turned
out to be incorrect.

Fixes: a9f85f93 ("firmware: imx: add COMPILE_TEST support")
Fixes: 5b00b837 ("firmware: imx: add COMPILE_TEST for IMX_SCU driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200408190314.695067-1-arnd@arndb.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/firmware/imx/Kconfig

@@ -12,7 +12,7 @@ config IMX_DSP
 
 config IMX_SCU
 	bool "IMX SCU Protocol driver"
-	depends on IMX_MBOX || COMPILE_TEST
+	depends on IMX_MBOX
 	help
 	  The System Controller Firmware (SCFW) is a low-level system function
 	  which runs on a dedicated Cortex-M core to provide power, clock, and
@@ -24,6 +24,6 @@ config IMX_SCU
 
 config IMX_SCU_PD
 	bool "IMX SCU Power Domain driver"
-	depends on IMX_SCU || COMPILE_TEST
+	depends on IMX_SCU
 	help
 	  The System Controller Firmware (SCFW) based power domain driver.