arch/mips: add support for MIPS32 FP mode

MIPS32 support different FP modes (32,xx,64), so give the user the
opportunity to choose between them. That will cause host-gcc to be built
using the --with-fp-32=[32|xx|64] configure option. Also the
-mfp[32|xx|64] gcc option will be added to TARGET_CFLAGS and to the
toolchain wrapper.

FP mode option shouldn't be used for soft-float, so we add logic in the
toolchain wrapper if -msoft-float is among the arguments in order to not
append the -fp[[32|xx|64] option, otherwise the compilation may fail.

Information about FP modes here:

- https://sourceware.org/binutils/docs/as/MIPS-Options.html
- https://dmz-portal.imgtec.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#5._Generating_modeless_code

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

toolchain/toolchain-wrapper.c

@@ -254,6 +254,20 @@ int main(int argc, char **argv)
 		*cur++ = "-mfloat-abi=" BR_FLOAT_ABI;
 #endif
 
+#ifdef BR_FP32_MODE
+	/* add fp32 mode if soft-float is not args or hard-float overrides soft-float */
+	int add_fp32_mode = 1;
+	for (i = 1; i < argc; i++) {
+		if (!strcmp(argv[i], "-msoft-float"))
+			add_fp32_mode = 0;
+		else if (!strcmp(argv[i], "-mhard-float"))
+			add_fp32_mode = 1;
+	}
+
+	if (add_fp32_mode == 1)
+		*cur++ = "-mfp" BR_FP32_MODE;
+#endif
+
 #if defined(BR_ARCH) || \
     defined(BR_CPU)
 	/* Add our -march/cpu flags, but only if none of