Kconfig: lay groundwork for not assuming SPI flash boot device

Almost all boards and chipsets within the codebase assume or
use SPI flash as the boot device. Therefore, provide an option
for the boards/chipsets which don't currently support SPI flash
as the boot device. The default is to assume SPI flash is the
boot device unless otherwise instructed. This falls in line
with the current assumptions, but it also allows one to
differentiate a platform desiring SPI flash support while it not
being the actual boot device.

One thing to note is that while google/daisy does boot with SPI
flash part no SPI API interfaces were ever implemented. Therefore,
mark that board as not having a SPI boot device.

BUG=chrome-os-partner:56151

Change-Id: Id4e0b4ec5e440e41421fbb6d0ca2be4185b62a6e
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/16191
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/emulation/qemu-armv7/Kconfig

@@ -31,6 +31,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select ARCH_ROMSTAGE_ARMV7
 	select ARCH_RAMSTAGE_ARMV7
 	select BOARD_ROMSIZE_KB_4096
+	select BOOT_DEVICE_NOT_SPI_FLASH
 
 config MAINBOARD_DIR
 	string

src/mainboard/emulation/qemu-power8/Kconfig

@@ -23,6 +23,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select ARCH_BOOTBLOCK_POWER8
 	select HAVE_UART_SPECIAL
 	select ARCH_POWER8
+	select BOOT_DEVICE_NOT_SPI_FLASH
 
 config MAINBOARD_DIR
 	string

src/mainboard/emulation/qemu-riscv/Kconfig

@@ -23,6 +23,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select BOARD_ROMSIZE_KB_4096
 	select ARCH_BOOTBLOCK_RISCV
 	select HAVE_UART_SPECIAL
+	select BOOT_DEVICE_NOT_SPI_FLASH
 
 config MAINBOARD_DIR
 	string

src/mainboard/emulation/spike-riscv/Kconfig

@@ -23,6 +23,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select BOARD_ROMSIZE_KB_4096
 	select ARCH_BOOTBLOCK_RISCV
 	select DRIVERS_UART_8250MEM
+	select BOOT_DEVICE_NOT_SPI_FLASH
 
 config MAINBOARD_DIR
 	string