Move ARCH_* from board/Kconfig to cpu or soc Kconfig.

CONFIG_ARCH is a property of the cpu or soc rather than a property of the
board. Hence, move ARCH_* from every single board to respective cpu or soc
Kconfigs. Also update abuild to ignore ARCH_ from mainboards.

Change-Id: I6ec1206de5a20601c32d001a384a47f46e6ce479
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: http://review.coreboot.org/5570
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/soc/Kconfig

@@ -1,3 +1 @@
-if ARCH_X86
 source src/soc/intel/Kconfig
-endif

src/soc/intel/baytrail/Kconfig

@@ -8,6 +8,7 @@ if SOC_INTEL_BAYTRAIL
 
 config CPU_SPECIFIC_OPTIONS
 	def_bool y
+	select ARCH_X86
 	select CACHE_MRC_SETTINGS
 	select CAR_MIGRATION
 	select COLLECT_TIMESTAMPS