Build: Remove +nofp option for Armv6-M from GNUARM

GNUARM doesn't support +nofp option for Armv6-M.
Add an exception for Armv6-M while adding +nofp in GNUARM >= v8.0

Change-Id: I100c8452718496910a210d9b1a18340c35503cb9
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/toolchain_GNUARM.cmake b/toolchain_GNUARM.cmake
index 9c06868..4a1e1b2 100644
--- a/toolchain_GNUARM.cmake
+++ b/toolchain_GNUARM.cmake
@@ -77,7 +77,8 @@
         endif()
         if(GCC_VERSION VERSION_GREATER_EQUAL "8.0.0")
             if (DEFINED CONFIG_TFM_SPE_FP)
-                if(CONFIG_TFM_SPE_FP STREQUAL "0")
+                if(CONFIG_TFM_SPE_FP STREQUAL "0" AND
+                   NOT TFM_SYSTEM_ARCHITECTURE STREQUAL "armv6-m")
                     string(APPEND CMAKE_SYSTEM_PROCESSOR "+nofp")
                 endif()
             endif()