kconfig: fix new choices being skipped upon config update

Running `oldconfig' after any of the following configuration change:

either trivial addition, such as:

config A
	bool "A"

choice
	prompt "Choice ?"
	depends on A

	config CHOICE_B
		bool "Choice B"

	config CHOICE_C
		bool "Choice C"
endchoice

or more tricky change:

OLD KCONFIG                      |  NEW KCONFIG
                                 |
                                 |  config A
                                 |          bool "A"
                                 |
choice                           |  choice
        prompt "Choice ?"        |          prompt "Choice ?"
                                 |
        config CHOICE_C          |          config CHOICE_C
                bool "Choice C"  |                  bool "Choice C"
                                 |
        config CHOICE_D          |          config CHOICE_D
                bool "Choice D"  |                  bool "Choice D"
endchoice                        |
                                 |          config CHOICE_E
                                 |                  bool "Choice E"
                                 |                  depends on A
                                 |  endchoice

will not cause the choice to be considered as NEW, and thus not be
asked. The cause of this behavior is that choice's novelty are computed
statically right after the saved configuration has been read. At this
point, the new dependency's value is still unknown and asserted to be
`no'. Moreover, no update to this decision is made afterward.

Correct this by dynamically evaluating a choice's novelty, and removing the
static evaluation.

Reported-and-tested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>