xtensa: add support for the Xtensa architecture

The Xtensa architecture had been removed because it required special
handling and depended on additional directories and files that became
obsolete over time. This change is more aligned to other architectures.

[Thomas: rebased on top of the "arch: improve definition of gcc mtune,
mcpu, etc." patch].

Signed-off-by: Chris Zankel <chris@zankel.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

arch/Config.in

@@ -145,6 +145,13 @@ config BR2_x86_64
 	  architecture compatible microprocessor).
 	  http://en.wikipedia.org/wiki/X86_64
 
+config BR2_xtensa
+	bool "Xtensa"
+	help
+	  Xtensa is a Tensilica processor IP architecture.
+	  http://en.wikipedia.org/wiki/Xtensa
+	  http://www.tensilica.com/
+
 endchoice
 
 # The following string values are defined by the individual
@@ -210,3 +217,7 @@ endif
 if BR2_i386 || BR2_x86_64
 source "arch/Config.in.x86"
 endif
+
+if BR2_xtensa
+source "arch/Config.in.xtensa"
+endif

arch/Config.in.xtensa

@@ -0,0 +1,2 @@
+config BR2_ARCH
+	default "xtensa"	if BR2_xtensa