mmc: tmio: Make DMA transfer end bit configurable

Different versions of the SDHI core use either bit 17 or bit 20 for the
DTRAEND indication, which can differ even between SoC revisions. Make
the DTRAEND bit position part of the driver private data, so that the
probe function can set this accordingly. Set this to 20 on Socionext
SoCs and either 17 or 20 on Renesas SoCs, depending on the SoC.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>