ubsan: use a big if block in Kconfig ...

A side effect (which was the motivation for this change) is that the
config item CONFIG_UBSAN_ALIGNMENT doesn't appear in configurations that
have CONFIG_UBSAN disabled.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

common: add generic CONFIG_UBSAN plumbing ...

-fsanitize=undefined allows compile-time instrumentation of code to detect
some classes of runtime undefined behavior.

In preparation for allowing arches to provide infrastructure in support
of this feature, add some generic UBSAN options and associated plumbing.

These are only shown in the debug menu when the arch selects the
appropriate symbol. The option is named equally to their Linux counterparts.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>