Unhide DEBUG_BUGVERBOSE when EXPERT=y, even if DEBUG_KERNEL=n

CONFIG_DEBUG_BUGVERBOSE defaults to y.  Embedded systems might want to
disable this to save space; however, disabling it requires enabling
CONFIG_DEBUG_KERNEL to see it.  Unhide it for CONFIG_EXPERT=y as well,
so it shows up as an option for embedded users without having to turn on
CONFIG_DEBUG_KERNEL.

Also make the option show up if CONFIG_DEBUG_KERNEL=y and
CONFIG_EXPERT=n, which seems sensible for a debug feature.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
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To me, it seemed highly counterintuitive to have to enable
CONFIG_DEBUG_KERNEL in order to *disable* debugging features; hence this
patch to expose one of the two that defaults to y.