libmad: disable ASO support for thumb-only ARM cores

Fixes:
http://autobuild.buildroot.net/results/8d4/8d4ea8613487297f2c33f3b9cbd8903cfb96e4c6/

The ARM specific optimizations enabled by LIBMAD_ASO needs classic ARM
instructions support, so disable for thumb-only cores.

[Peter: don't drop default y as pointed out by Baruch Siach]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libmad/Config.in

@@ -37,6 +37,8 @@ config BR2_PACKAGE_LIBMAD_SSO
 
 config BR2_PACKAGE_LIBMAD_ASO
 	bool "Architecture-specific optimizations"
+	# arm optimization needs classic arm instructions support
+	depends on !(BR2_arm && !BR2_ARM_CPU_HAS_ARM)
 	default y
 	help
 	  Use certain architecture-specific optimizations.