testsuite: arm: Use effective-target for nomve_fp_1.c test

Update test cases to use -mcpu=unset/-march=unset feature introduced in
r15-3606-g7d6c6a0d15c.

gcc/testsuite/ChangeLog:

	* g++.target/arm/mve/general-c++/nomve_fp_1.c: Added option
	"-mcpu=unset".

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>

gcc/testsuite/g++.target/arm/mve/general-c++/nomve_fp_1.c

@@ -4,7 +4,7 @@
 /* Do not use dg-add-options arm_v8_1m_mve, because this might expand to "",
    which could imply mve+fp depending on the user settings. We want to make
    sure the '+fp' extension is not enabled.  */
-/* { dg-options "-mfpu=auto -march=armv8.1-m.main+mve" } */
+/* { dg-options "-mfpu=auto -mcpu=unset -march=armv8.1-m.main+mve" } */
 /* { dg-add-options arm_fp } */
 
 #include <arm_mve.h>