libpayload: Minor board ID / RAM code cleanups

This patch mirrors recent cleanups in coreboot regarding the strapping
ID entries in the coreboot table.

Change-Id: Ia5c3728daf2cb317f8e2bc72c6f1714d6cb4d080
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/22742
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

payloads/libpayload/include/sysinfo.h

@@ -108,8 +108,11 @@ struct sysinfo_t {
 	void		*cbmem_cons;
 	void		*mrc_cache;
 	void		*acpi_gnvs;
+
+#define UNDEFINED_STRAPPING_ID (~0)
 	u32		board_id;
 	u32		ram_code;
+
 	void		*wifi_calibration;
 	uint64_t	ramoops_buffer;
 	uint32_t	ramoops_buffer_size;