armcm_reset: Introduce Kconfig FLASH_BOOT_ADDRESS value

Specify the arm architecture flash bootup address for each chip type
in Kconfig using a new FLASH_BOOT_ADDRESS setting.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/atsamd/usbserial.c

@@ -5,7 +5,7 @@
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
 #include <string.h> // memcpy
-#include "autoconf.h" // CONFIG_FLASH_START
+#include "autoconf.h" // CONFIG_MACH_SAMD21
 #include "board/armcm_boot.h" // armcm_enable_irq
 #include "board/io.h" // writeb
 #include "board/usb_cdc.h" // usb_notify_ep0