kconfig: Replace some single-symbol 'if's with 'depends on'

I think people might be reading differences into 'if' and 'depends on'
that aren't there, like maybe 'if' being needed to "hide" a symbol,
while 'depends on' just adds a dependency.

There are no differences between 'if' and 'depends on'. 'if' is just a
shorthand for 'depends on'. They work the same when it comes to creating
implicit menus too.

The way symbols get "hidden" is through their dependencies not being
satisfied ('if'/'depends on' get copied up as a dependency on the
prompt).

Since 'if' and 'depends on' are the same, an 'if' with just a single
symbol in it can be replaced with a 'depends on'. IMO, it's best to
avoid 'if' there as a style choice too, because it confuses people into
thinking there's deep Kconfig magic going on that requires 'if'.

Going for 'depends on' can also remove some nested 'if's, which
generates nicer symbol information and docs, because nested 'if's really
are so simple/dumb that they just add the dependencies from both 'if's
to all symbols within.

Replace a bunch of single-symbol 'if's with 'depends on' to despam the
Kconfig files a bit and make it clearer how things work. Also do some
other minor related dependency refactoring.

The replacement isn't complete. Will fix up the rest later. Splitting it
a bit to make it more manageable.

(Everything above is true for choices, menus, and comments as well.)

Detected by tweaking the Kconfiglib parsing code. It's impossible to
detect after parsing, because 'if' turns into 'depends on'.

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

subsys/shell/Kconfig

@@ -101,16 +101,13 @@ config SHELL_HISTORY
 	  Enable commands history. History can be accessed using up and down
 	  arrows.
 
-if SHELL_HISTORY
-
 config SHELL_HISTORY_BUFFER
 	int "History buffer in bytes"
 	default 512
+	depends on SHELL_HISTORY
 	help
 	  Number of bytes dedicated for storing executed commands.
 
-endif # SHELL_HISTORY
-
 config SHELL_STATS
 	bool "Enable shell statistics"
 	default y