kconfig: Remove redundant 'default n' and 'prompt' 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.

Also replace some

    config
    	prompt "foo"
    	bool/int

with the more common shorthand

    config
    	bool/int "foo"

See the 'Style recommendations and shorthands' section in
https://docs.zephyrproject.org/latest/guides/kconfig/index.html

.

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