mmc: arm_pl180_mmci: Sync compatible with kernel

Initially the compatible string was wrongly set to "st,stm32f4xx-sdio".
Use compatible string used by kernel instead and identify mmci variant
using "arm,primecell-periphid" property.

Currently, the DM part of mmci driver is only used by STM32 SoCs,
that's why the switch case gets only one entry. It will be populated
easily with new variant in the future.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>