Disable use of Neon VFP support for platform stm32mp1 when
building with SP_MIN runtime services as these can conflict with
non-secure world use of NEON support. This is preferred over a
systematic backup/restore of NEON context when switching
between non-secure and secure worlds.

When NEON support is disabled, this is done for both BL2 and BL32 as
build process uses common libraries built once for both binaries.

Change-Id: I4e8808dcb6ef58fc839e6f85fd6e45cfbaa34be0
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>