soc: apple: apple-pmgr-pwrstate: Do not build as a module

This doesn't make any sense as a module since it is a critical device,
and it turns out of_phandle_iterator_args was not exported so the module
version doesn't build anyway.

Fixes: 6df9d38f9146 ("soc: apple: Add driver for Apple PMGR power state controls")
Reported-by: kernel test robot <[e-mail]>
Reviewed-by: Sven Peter <[e-mail]>
Signed-off-by: Hector Martin <[e-mail]>

drivers/soc/apple/Kconfig

···
 menu "Apple SoC drivers"
 
 config APPLE_PMGR_PWRSTATE
-	tristate "Apple SoC PMGR power state control"
+	bool "Apple SoC PMGR power state control"
 	depends on PM
 	select REGMAP
 	select MFD_SYSCON