drivers: ipm: Kconfig: Remove redundant 'default n' properties

Bool symbols implicitly default to 'n'.

A 'default n' can make sense e.g. in a Kconfig.defconfig file, if you
want to override a 'default y' on the base definition of the symbol. It
isn't used like that on any of these symbols though, and is
inconsistent.

This will make the auto-generated Kconfig documentation have "No
defaults. Implicitly defaults to n." as well, which is clearer than
'default n if ...'

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

drivers/ipm/Kconfig

@@ -1,21 +1,18 @@
 menuconfig IPM
 	bool
 	prompt "IPM drivers"
-	default n
 	help
 	  Include interrupt-based inter-processor mailboxes
 	  drivers in system configuration
 
 config IPM_QUARK_SE
 	bool "Quark SE IPM driver"
-	default n
 	depends on IPM
 	help
 	  Driver for Quark SE mailboxes
 
 config IPM_QUARK_SE_MASTER
 	bool "Quark SE IPM master controller"
-	default n
 	depends on IPM_QUARK_SE
 	help
 	  Enable this for the first CPU that initializes IPM.
@@ -24,7 +21,6 @@ config IPM_QUARK_SE_MASTER
 
 config IPM_MCUX
 	bool "MCUX IPM driver"
-	default n
 	depends on IPM && HAS_MCUX
 	help
 	  Driver for MCUX mailbox