mmc: mmci: add validate_data callback

This patch adds validate_data callback at mmci_host_ops
to check specific constraints of variant.
Move mmci_validate_data function to regroup mmci_host_ops interfaces.

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>