Kconfig: Introducing ARCH_CHOICE symbol for Architecture choice group

The ARCH_CHOICE symbol on the arch/Kconfig choice for Architecture
selection, allows for multiple definitions of the choice group which
makes it possible for out-of-tree architectures to add entries to the
list as needed.

For example, in $(ARCH_DIR)/$(ARCH)/Kconfig by adding something like;

choice ARCH_CHOICE
config xARCH
	bool "xARCH architecture"
endchoice

No functional change expected.

Signed-off-by: Danny Oerndrup <daor@demant.com>

arch/Kconfig

@@ -14,7 +14,7 @@
 # Note: $ARCH might be a glob pattern
 source "$(ARCH_DIR)/$(ARCH)/Kconfig"
 
-choice
+choice ARCH_CHOICE
 	prompt "Architecture"
 	default X86