drivers/i2c/at24rf08c: Add proper Kconfig option

The existing Kconfig code made SMBIOS_PROVIDED_BY_MOBO depend
on VENDOR_LENOVO. Thus, it couldn't be selected by boards from
other vendors. So we add another Kconfig that selects it
here.

NB. It's still unclear how the two drivers in this directory
are related (at24rf08c and lenovo_serial). From the code, it
doesn't look like the latter belongs here.

Change-Id: Iaa5c5a584f2a5e2426352ec6aa681f99a55efa49
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35472
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/i2c/at24rf08c/Kconfig

@@ -1,7 +1,4 @@
-if VENDOR_LENOVO
-
-config SMBIOS_PROVIDED_BY_MOBO
+config DRIVER_LENOVO_SERIALS
 	bool
-	default y
-
-endif
+	default y if VENDOR_LENOVO
+	select SMBIOS_PROVIDED_BY_MOBO

src/drivers/i2c/at24rf08c/Makefile.inc

@@ -1,2 +1,2 @@
-ramstage-$(CONFIG_VENDOR_LENOVO) += at24rf08c.c
-ramstage-$(CONFIG_VENDOR_LENOVO) += lenovo_serials.c
+ramstage-$(CONFIG_DRIVER_LENOVO_SERIALS) += at24rf08c.c
+ramstage-$(CONFIG_DRIVER_LENOVO_SERIALS) += lenovo_serials.c