mmc: stm32_sdmmc2: Update DT properties with v4.19 bindings

Some properties name has been updated:
  - st,dirpol becomes st,sig-dir
  - st,negedge becomes st,neg-edge
  - st,pin-ckin becomes st,use-ckin

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>