bootmem: Clarify usage with bounce-buffer

Add bootmem_targets_usable_with_bounce() to handle
cases of payload loading via bounce-buffer.

Change-Id: I9ebbc621f8810c0317d7c97c6b4cdd41527ddcbb
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/26985
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/bootmem.h

@@ -97,6 +97,11 @@ bool bootmem_walk(range_action_t action, void *arg);
 /* Return 1 if region targets usable RAM, 0 otherwise. */
 int bootmem_region_targets_usable_ram(uint64_t start, uint64_t size);
 
+/* Return 1 if region targets usable RAM, and we allow memory ranges
+ * with type >BM_MEM_OS_CUTOFF to be overwritten at the time we jump
+ * to payload. 0 otherwise. */
+int bootmem_region_usable_with_bounce(uint64_t start, uint64_t size);
+
 /* Allocate a temporary buffer from the unused RAM areas. */
 void *bootmem_allocate_buffer(size_t size);