commonlib: Add function to hash contents of a CBFS region.

Provide a common routine to hash the contents of a cbfs
region. The cbfs region is hashed in the following order:
1. potential cbfs header at offset 0
2. potential cbfs header retlative offset at cbfs size - 4
3. For each file the metadata of the file.
4. For each non-empty file the data of the file.

BUG=chrome-os-partner:48412
BUG=chromium:445938
BRANCH=None
TEST=Utilized in chromeos cros_bundle_firmware as well as at
      runtime during vboot verification on glados.

Change-Id: Ie1e5db5b8a80d9465e88d3f69f5367d887bdf73f
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/12786
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)

src/vendorcode/amd/pi/Makefile.inc

@@ -62,6 +62,7 @@ AGESA_INC += -I$(src)/southbridge/amd/pi/hudson
 AGESA_INC += -I$(src)/arch/x86/include
 AGESA_INC += -I$(src)/include
 AGESA_INC += -I$(src)/commonlib/include
+AGESA_INC += -I$(VB_SOURCE)/firmware/include
 
 AGESA_CFLAGS += -march=amdfam10 -mno-3dnow -fno-zero-initialized-in-bss -fno-strict-aliasing
 CFLAGS_x86_32 += $(AGESA_CFLAGS)

src/vendorcode/google/chromeos/Makefile.inc

@@ -49,6 +49,4 @@ else
 CFLAGS_common += -DMOCK_TPM=0
 endif
 
-VB_SOURCE ?= 3rdparty/vboot
 subdirs-$(CONFIG_VBOOT_VERIFY_FIRMWARE) += vboot2
-CPPFLAGS_common += -I$(VB_SOURCE)/firmware/include