libpayload: Implement new CBFS access API

This commit adds new CBFS API, which is based on the one available in
the main coreboot source tree. Libpayload implementation supports RO/RW
file lookups and file contents verification.

Change-Id: I00da0658dbac0cddf92ad55611def947932d23c7
Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59497
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

payloads/libpayload/tests/mocks/die.c

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <tests/test.h>
+#include <stdbool.h>
+
+void die_work(const char *file, const char *func, int line, const char *fmt, ...)
+{
+	/* Failing asserts are jumping to the user code (test) if expect_assert_failed() was
+	   previously called. Otherwise it jumps to the cmocka code and fails the test. */
+	mock_assert(false, "Mock assetion called", file, line);
+
+	/* Should never be reached */
+	print_error("%s() called...\n", __func__);
+	while (1)
+		;
+}