This patch allows to define specific pio mask for variants.
Needed to support the STM32 sdmmc variant which has some bits
with different meaning (bits: 21,20,13,12,9)
Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>