Replace direct printf calls in malloc_dump() with an output callback
function. This introduces dump_out_fn type and dump_to_console() helper,
with malloc_dump_impl() taking the callback and context pointer.
This allows the same implementation logic to be reused for different
output destinations such as writing to a file.
Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
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