serial: sh-sci: Improve DMA error messages

Make the life of the driver developer/debugger easier:
  - Add __func__ prefix to identical messages,
  - Add DMA directions to messages,
  - Add TX failure messages,
  - Always use "cookie %d" for DMA cookies,
  - "#%d" is reserved for the DMA cookie/descriptor index.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>