cbfs: Rename CBFS_TYPE_PAYLOAD to CBFS_TYPE_SELF

In preparation of having FIT payloads, which aren't converted to simple ELF,
rename the CBFS type payload to actually show the format the payload is
encoded in.

Another type CBFS_TYPE_FIT will be added to have two different payload
formats. For now this is only a cosmetic change.

Change-Id: I39ee590d063b3e90f6153fe655aa50e58d45e8b0
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/25986
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

payloads/libpayload/include/cbfs_core.h

@@ -67,7 +67,7 @@
     components */
 
 #define CBFS_TYPE_STAGE      0x10
-#define CBFS_TYPE_PAYLOAD    0x20
+#define CBFS_TYPE_SELF       0x20
 #define CBFS_TYPE_OPTIONROM  0x30
 #define CBFS_TYPE_BOOTSPLASH 0x40
 #define CBFS_TYPE_RAW        0x50