manifest: added missed AOSP tree : external/eigen

Change-Id: Id94a1b65cf3e6cafe133a4c559d0087995971f4d
Signed-off-by: Arnav Gupta <championswimmer@aokp.co>
Merge "manifest: added missed AOSP tree : external/eigen" into jb-mr2

Conflicts:
	default.xml

Change-Id: I29ef90420bb88650767c02ad46e2cad834c3857d