soc/amd/stoneyridge: select RTC

Stoneyridge has an RTC. Elog requires it for timestamps.

BUG=b:65485690
TEST=Build Kahlee with Elog. Check mosys eventlog list for
timestamps.

Change-Id: I4d820fbe11043e7e3153d67159f52274d5f14bae
Signed-off-by: Marc Jones <marcj303@gmail.com>
Reviewed-on: https://review.coreboot.org/22961
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/soc/amd/stoneyridge/Kconfig

@@ -64,6 +64,7 @@ config CPU_SPECIFIC_OPTIONS
 	select POSTCAR_CONSOLE
 	select SSE
 	select SSE2
+	select RTC
 
 config VBOOT
 	select VBOOT_SEPARATE_VERSTAGE