lib/imd_cbmem.c: Add a helper function to indicate that cbmem is ready

This can be used in romstage in particular to know if dram is ready.

Change-Id: I0231ab9c0b78a69faa762e0a97378bf0b50eebaf
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38736
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/lib/imd_cbmem.c

@@ -30,6 +30,8 @@ void *cbmem_top(void)
 	dead_code();
 }
 
+int cbmem_initialized;
+
 static inline const struct cbmem_entry *imd_to_cbmem(const struct imd_entry *e)
 {
 	return (const struct cbmem_entry *)e;
@@ -79,6 +81,8 @@ void cbmem_initialize_empty_id_size(u32 id, u64 size)
 
 	/* Complete migration to CBMEM. */
 	cbmem_run_init_hooks(no_recovery);
+
+	cbmem_initialized = 1;
 }
 
 int cbmem_initialize(void)
@@ -112,6 +116,8 @@ int cbmem_initialize_id_size(u32 id, u64 size)
 	/* Complete migration to CBMEM. */
 	cbmem_run_init_hooks(recovery);
 
+	cbmem_initialized = 1;
+
 	/* Recovery successful. */
 	return 0;
 }