stm32mp1: remove the imply BOOTSTAGE

This patch is only a temporarily workaround for crash introduced by
commit ac9cd480 ("bootstage: Correct relocation algorithm").

The crash occurs because the bootstage struct is not correctly aligned
when BOOTSTAGE feature is activated.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Acked-by: Patrick Delaunay <patrick.delaunay@st.com>