feat(st-sdmmc2): allow compatible to be defined in platform code

Put DT_SDMMC2_COMPAT under #ifndef. Keep the default value if it is not
defined in platform code.

Change-Id: I611baaf1fc622d33e655ee2c78d9c287baaa6a67
Signed-off-by: Yann Gautier <yann.gautier@st.com>
1 file changed