mmc: mmci: internalize dma map/unmap into mmci dma functions

This patch internalizes the management of dma map/unmap into
mmci dma interfaces. This allows to simplify and prepare the next dma
callbacks for mmci host ops.
mmci_dma_unmap was called in mmci_data_irq & mmci_cmd_irq functions
and can be integrated in mmci_dma_data_error.

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>