libcr51sign: import from gBMC

Validate the cr51 descriptor of the BIOS image. It can also
parse the BIOS version and write it to a file.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: I098be66b228da6f3514d3f13166a1bb4e1e718fb
diff --git a/.gitignore b/.gitignore
index 210bc0f..d73d627 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 build*/
 subprojects/*
 !subprojects/acpi-power-state-daemon/
+!subprojects/libcr51sign/
 !subprojects/metrics-ipmi-blobs/
 !subprojects/ncsid/
 !subprojects/nemora-postd/