peppy: Re-enable EC software sync

The EC was disabling flash commands and sysjump was not working
properly. With those two fixed software sync works properly.
(Taken from I63ca00d6c94854f2b395eb736ce20792da5f8de2).

Change-Id: I9c7d1d1f1aaf7de33d0cec5f6daf648576ba8900
Reviewed-on: https://gerrit.chromium.org/gerrit/57289
Reviewed-by: Dave Parker <dparker@chromium.org>
Commit-Queue: Shawn Nematbakhsh <shawnn@chromium.org>
Tested-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-on: http://review.coreboot.org/4212
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/google/peppy/Kconfig

@@ -9,6 +9,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select INTEL_LYNXPOINT_LP
 	select BOARD_ROMSIZE_KB_8192
 	select EC_GOOGLE_CHROMEEC
+	select EC_SOFTWARE_SYNC
 	select HAVE_ACPI_TABLES
 	select HAVE_OPTION_TABLE
 	select HAVE_ACPI_RESUME