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/cpu/amd/agesa/Kconfig

@@ -26,6 +26,7 @@ config CPU_AMD_AGESA
 	default y if CPU_AMD_AGESA_FAMILY15_TN
 	default y if CPU_AMD_AGESA_FAMILY16_KB
 	default n
+	select ARCH_X86
 	select TSC_SYNC_LFENCE
 	select UDELAY_LAPIC
 	select LAPIC_MONOTONIC_TIMER