drivers/spi: Remove Kconfig prompt from SPI_FLASH_SMM

Why would that be a user visible option? Drop the prompt and the
`default n` and select it automatically when needed. I hope I
caught all its users.

TEST=Confirmed that systems with ELOG_GSMI or DEBUG_SMI compile
     and link.

Change-Id: I44aeec530cc333f4ed4c8cfe67c7b5c9d8fb0049
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/26872
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/drivers/elog/Kconfig

@@ -41,6 +41,7 @@ endif
 config ELOG_GSMI
 	depends on ELOG && SMM_TSEG
 	bool "SMI interface to write and clear event log"
+	select SPI_FLASH_SMM if BOOT_DEVICE_SPI_FLASH_RW_NOMMAP
 	default n
 	help
 	  This interface is compatible with the linux kernel driver