CBMEM: Clarify CBMEM_TOP_BACKUP function usage

The deprecated LATE_CBMEM_INIT function is renamed:
  set_top_of_ram -> set_late_cbmem_top

Obscure term top_of_ram is replaced:
  backup_top_of_ram -> backup_top_of_low_cacheable
  get_top_of_ram -> restore_top_of_low_cacheable

New function that always resolves to CBMEM top boundary, with
or without SMM, is named restore_cbmem_top().

Change-Id: I61d20f94840ad61e9fd55976e5aa8c27040b8fb7
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/19377
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>
diff --git a/src/include/cbmem.h b/src/include/cbmem.h
index 21ca097..68f3615 100644
--- a/src/include/cbmem.h
+++ b/src/include/cbmem.h
@@ -151,12 +151,15 @@
  * value stored in nvram to enable early recovery on S3 path.
  */
 #if IS_ENABLED(CONFIG_ARCH_X86)
-/* Note that many of the current providers of get_top_of_ram() conditionally
- * return 0 when the sleep type is non S3. i.e. cold and warm boots would
- * return 0 from get_top_of_ram(). */
-unsigned long get_top_of_ram(void);
-void set_top_of_ram(uint64_t ramtop);
-void backup_top_of_ram(uint64_t ramtop);
+/* Note that with LATE_CBMEM_INIT, restore_top_of_low_cacheable()
+ * may conditionally return 0 when the sleep type is non S3,
+ * i.e. cold and warm boots would return NULL also for cbmem_top. */
+void backup_top_of_low_cacheable(uintptr_t ramtop);
+uintptr_t restore_top_of_low_cacheable(void);
+uintptr_t restore_cbmem_top(void);
+
+/* Deprecated, only use with LATE_CBMEM_INIT. */
+void set_late_cbmem_top(uintptr_t ramtop);
 #endif
 
 /*