drm/bridge: ti-sn65dsi86: Fix auxiliary bus lifetime

Memory for the "struct device" for any given device isn't supposed to
be released until the device's release() is called. This is important
because someone might be holding a kobject reference to the "struct
device" and might try to access one of its members even after any
other cleanup/uninitialization has happened.

Code analysis of ti-sn65dsi86 shows that this isn't quite right. When
the code was written, it was believed that we could rely on the fact
that the child devices would all be freed before the parent devices
and thus we didn't need to worry about a release() function. While I
still believe that the parent's "struct device" is guaranteed to
outlive the child's "struct device" (because the child holds a kobject
reference to the parent), the parent's "devm" allocated memory is a
different story. That appears to be freed much earlier.

Let's make this better for ti-sn65dsi86 by allocating each auxiliary
with kzalloc and then free that memory in the release().

Fixes: bf73537f411b ("drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers")
Suggested-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613065812.v2.1.I24b838a5b4151fb32bccd6f36397998ea2df9fbb@changeid

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