[RFC] mci: add DSR support

[Markus Niebel]

This is an example to add DSR support to barebox. Why this feature is
considered as useful is described in the first patch. Second patch shows
how to pass values and third patch shows how this can be supported for
a board.

Tested with TQMa53 and a 4.41 Micron eMMC with DSR support.

[PATCH 1/3] mci: add DSR support
[PATCH 2/3] mci: imx-esdhc: add DSR support
[PATCH 3/3] boards: tqma53: add DSR support for eMMC