cbfs_spi: enable CBFS access in early romstage

Currently the CBFS mmap cannot be accessed at the beginning of romstage
because it waits until DRAM is initialized. This change first loads CBFS
into SRAM and then switches to using DRAM as the backing once it is
initialized.

BUG=chromium:210230
BRANCH=none
TEST=confirm that the cbfs can be access at the beginning and end of
romstage on different boards.

Change-Id: I9fdaef392349c27ba1c19d4cd07e8ee0ac92dddc
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: ccaaba266386c7d5cc62de63bdca81a0cc7c4d83
Original-Change-Id: Idabfab99765b52069755e1d1aa61bbee39501796
Original-Signed-off-by: Mary Ruthven <mruthven@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/312577
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/12586
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/src/include/symbols.h b/src/include/symbols.h
index 52fea48..bf875ae 100644
--- a/src/include/symbols.h
+++ b/src/include/symbols.h
@@ -41,6 +41,10 @@
 extern u8 _estack[];
 #define _stack_size (_estack - _stack)
 
+extern u8 _dram_cbfs_cache[];
+extern u8 _edram_cbfs_cache[];
+#define _dram_cbfs_cache_size (_edram_cbfs_cache - _dram_cbfs_cache)
+
 extern u8 _cbfs_cache[];
 extern u8 _ecbfs_cache[];
 #define _cbfs_cache_size (_ecbfs_cache - _cbfs_cache)