arch/Config.in.x86: drastically simplify the BR2_ARCH definition

The BR2_ARCH definition is like this:

 * i486 for the i486 platform
 * i586 for a small number of platforms
 * i686 for all other x86 platforms when used in 32-bit, but we
   enumerate their entire list
 * x86_64 for all x86 64-bit platforms

The list for i686 is long and needs to be extended everytime a new
platform is added, with no added value.

So this commit simplifies that by replacing this long list with just:

   default "i686"	  if BR2_i386

This works because Kconfig guarantees us that if an i386 platform
matches an earlier case (i486 or one of the i586 platforms), the i486
and i586 earlier in the list will match.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

arch/Config.in.x86

@@ -311,30 +311,12 @@ config BR2_ARCH
 	default "i686"		if BR2_x86_c32
 	default "i586"		if BR2_x86_winchip_c6
 	default "i586"		if BR2_x86_winchip2
-	default "i686"		if BR2_x86_i686
-	default "i686"		if BR2_x86_pentium2
-	default "i686"		if BR2_x86_pentium3
-	default "i686"		if BR2_x86_pentium4
-	default "i686"		if BR2_x86_pentium_m
-	default "i686"		if BR2_x86_pentiumpro
-	default "i686"		if BR2_x86_prescott
-	default "i686"		if BR2_x86_nocona && BR2_i386
-	default "i686"		if BR2_x86_core2 && BR2_i386
-	default "i686"		if BR2_x86_corei7 && BR2_i386
-	default "i686"		if BR2_x86_westmere && BR2_i386
-	default "i686"		if BR2_x86_corei7_avx && BR2_i386
-	default "i686"		if BR2_x86_core_avx2 && BR2_i386
-	default "i686"		if BR2_x86_atom && BR2_i386
-	default "i686"		if BR2_x86_silvermont && BR2_i386
-	default "i686"		if BR2_x86_opteron && BR2_i386
-	default "i686"		if BR2_x86_opteron_sse3 && BR2_i386
-	default "i686"		if BR2_x86_barcelona && BR2_i386
-	default "i686"		if BR2_x86_jaguar && BR2_i386
-	default "i686"		if BR2_x86_steamroller && BR2_i386
-	default "i686"		if BR2_x86_k6
-	default "i686"		if BR2_x86_k6_2
-	default "i686"		if BR2_x86_athlon
-	default "i686"		if BR2_x86_athlon_4
+	# We use the property of Kconfig that the first match of a
+	# list of default will be chosen. So the following entry will
+	# not match for all BR2_i386=y configurations, but only the
+	# ones that didn't match any of the previous cases (i486,
+	# i586).
+	default "i686"		if BR2_i386
 	default "x86_64"	if BR2_x86_64
 
 config BR2_ENDIAN