stm32mp1: disable neon in sp_min

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>

plat/st/stm32mp1/platform.mk

@@ -16,6 +16,11 @@ PLAT_XLAT_TABLES_DYNAMIC :=	1
 $(eval $(call assert_boolean,PLAT_XLAT_TABLES_DYNAMIC))
 $(eval $(call add_define,PLAT_XLAT_TABLES_DYNAMIC))
 
+ifeq ($(AARCH32_SP),sp_min)
+# Disable Neon support: sp_min runtime may conflict with non-secure world
+TF_CFLAGS		+=      -mfloat-abi=soft
+endif
+
 # Not needed for Cortex-A7
 WORKAROUND_CVE_2017_5715:=	0