debug_uart: Try not to use stack in printch

debug_uart: Try not to use stack in printch

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Content preview:  Previous change to create _printch causes the stack to be
  used, breaking printch before stack is available. Inline _printch to prevent
   this happening. Signed-off-by: Tim Chick <tim.chick@mediatek.com> --- [...]

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Previous change to create _printch causes the stack to be used,
breaking printch before stack is available. Inline _printch to
prevent this happening.

Signed-off-by: Tim Chick <tim.chick@mediatek.com>