dpll: Make ZL3073X invisible

Currently, the user is always asked about the Microchip Azurite
DPLL/PTP/SyncE core driver, even when I2C and SPI are disabled, and thus
the driver cannot be used at all.

Fix this by making the Kconfig symbol for the core driver invisible
(unless compile-testing), and selecting it by the bus glue sub-drivers.
Drop the modular defaults, as drivers should not default to enabled.

Fixes: 2df8e64e01c10a4b ("dpll: Add basic Microchip ZL3073x support")
Signed-off-by: Geert Uytterhoeven <[e-mail]>
Link: https://patch.msgid.link/97804[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/dpll/zl3073x/Kconfig

···
 # SPDX-License-Identifier: GPL-2.0-only
 
 config ZL3073X
-	tristate "Microchip Azurite DPLL/PTP/SyncE devices"
+	tristate "Microchip Azurite DPLL/PTP/SyncE devices" if COMPILE_TEST
 	depends on NET
 	select DPLL
 	select NET_DEVLINK
···
 
 config ZL3073X_I2C
 	tristate "I2C bus implementation for Microchip Azurite devices"
-	depends on I2C && ZL3073X
+	depends on I2C
 	select REGMAP_I2C
-	default m
+	select ZL3073X
 	help
 	  This is I2C bus implementation for Microchip Azurite DPLL/PTP/SyncE
 	  devices.
···
 
 config ZL3073X_SPI
 	tristate "SPI bus implementation for Microchip Azurite devices"
-	depends on SPI && ZL3073X
+	depends on SPI
 	select REGMAP_SPI
-	default m
+	select ZL3073X
 	help
 	  This is SPI bus implementation for Microchip Azurite DPLL/PTP/SyncE
 	  devices.