mmc: mmci: Don't pretend all variants to have OPENDRAIN bit

This patch prepares for supporting STM32 variant which doesn't
have opendrain bit in MMCIPOWER register.
ST others variant (u300, nomadik and ux500) uses MCI_OD bit whereas
others variants uses MCI_ROD bit.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>