Added KERNEL_MASTER config flag

This makes it possible to statically check if the kernel is the master
kernel from user level. This is useful when when writing user level code
that's expected to work with different kernel versions.

Kconfig

@@ -20,6 +20,10 @@ config ARCH_ARM_V7A
     bool
     default n
 
+config KERNEL_MASTER
+    bool
+    default y
+
 # Native word size of the current platform. This is primarily intended for use
 # in code generators that need to know, at generation-time, the word size of
 # the target platform.