zio: improve zio DMA helpers

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
kernel: fix messages int format

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
kernel: remove debuggin timestamps

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
kernel: comments and minor style changes

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>