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/ti/am335x/Kconfig

@@ -1,5 +1,5 @@
 config CPU_TI_AM335X
-	depends on ARCH_ARMV7
+	select ARCH_ARMV7
 	select HAVE_MONOTONIC_TIMER
 	select HAVE_UART_SPECIAL
 	select BOOTBLOCK_CONSOLE