toolchain: select sensible floating point mode by default

Introduce BR2_PREFER_SOFT_FLOAT and enable it for arm, avr32 and mips,
and use it to enable soft float support by default for those archs.

This way people automatically get the correct floating point mode when
running make menuconfig for the first time (E.G. without a .config) and
changing the arch from i386 to arm/avr32/mips.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/Config.in.2

@@ -74,17 +74,20 @@ config BR2_USE_WCHAR
 	  If you have an external binary toolchain that has been built 
 	  with WCHAR support then enable this option.
 
+config BR2_PREFER_SOFT_FLOAT
+	bool
+	default y if BR2_arm || BR2_armeb || BR2_avr32 || BR2_mips || BR2_mipsel || BR2_nios2
+
 config BR2_SOFT_FLOAT
 	bool "Use software floating point by default"
 	depends on BR2_arm || BR2_armeb || BR2_avr32 || BR2_mips || BR2_mipsel || BR2_powerpc || BR2_nios2
+	default $(BR2_PREFER_SOFT_FLOAT)
 	help
 	  If your target CPU does not have a Floating Point Unit (FPU) or a
 	  kernel FPU emulator, but you still wish to support floating point
 	  functions, then everything will need to be compiled with soft
 	  floating point support (-msoft-float).
 
-	  Most people will answer N.
-
 config BR2_USE_SSP
 	bool "Enable stack protection support"
 	help