gcc: default to gcc 7.x, but not for sparc, linux kernel problem

target/config/Config.in.compiler

@@ -24,8 +24,8 @@ default ADK_TOOLCHAIN_GCC_4_4 if ADK_TARGET_ARCH_AVR32
 default ADK_TOOLCHAIN_GCC_4_9 if ADK_TARGET_ARCH_LM32 && !ADK_TARGET_LIB_NEWLIB
 default ADK_TOOLCHAIN_GCC_4_9 if ADK_TARGET_LIB_GLIBC && ADK_TARGET_ARCH_SH
 default ADK_TOOLCHAIN_GCC_4_9 if ADK_TARGET_SYSTEM_KINETIS_K70
-default ADK_TOOLCHAIN_GCC_7 if ADK_TARGET_ARCH_CRIS
-default ADK_TOOLCHAIN_GCC_6
+default ADK_TOOLCHAIN_GCC_6 if ADK_TARGET_ARCH_SPARC
+default ADK_TOOLCHAIN_GCC_7
 
 config ADK_TOOLCHAIN_GCC_GIT
 	bool "git"