mmc: matsushita-common: Handle DMA completion flag differences

The DMA READ completion flag position differs on Socionext and Renesas
SoCs. It is bit 20 on Socionext SoCs and using bit 17 is a hardware bug
and forbidden. It is bit 17 on Renesas SoCs and bit 20 does not work on
them.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>