Kconfig: separate memory mapped boot device from SPI

Make the indication of the boot device being memory mapped
separate from SPI. However, retain the same defaults that
previously existed.

BUG=chrome-os-partner:56151

Change-Id: Ibdd7c8754f9bf560a878136b1f55238e2c2549d3
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/16193
Reviewed-by: Andrey Petrov <andrey.petrov@intel.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/Kconfig

@@ -480,6 +480,13 @@ endmenu
 
 source "src/acpi/Kconfig"
 
+config BOOT_DEVICE_MEMORY_MAPPED
+	bool
+	default y if ARCH_X86 && BOOT_DEVICE_SPI_FLASH
+	default n
+	help
+	  Inform system if SPI is memory-mapped or not.
+
 config RTC
 	bool
 	default n