libpayload: Add fmap_cache to sysinfo_t

Now that FMAP is cached in CBMEM and its pointer is added to coreboot
table for quick lookup, this change adds a new member "fmap_cache" to
sysinfo_t that can be used by payloads to get to FMAP cache.

BUG=b:141723751

Change-Id: If894c20c2de89a9d8564561bc7780c86f3f4135a
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35640
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Shelley Chen <shchen@google.com>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

payloads/libpayload/include/sysinfo.h

@@ -128,6 +128,9 @@ struct sysinfo_t {
 	uint32_t mtc_size;
 	void	*chromeos_vpd;
 	int	mmc_early_wake_status;
+
+	/* Pointer to FMAP cache in CBMEM */
+	void	*fmap_cache;
 };
 
 extern struct sysinfo_t lib_sysinfo;