Building against warrior still needs efibootmgr from meta-oe

[ChinHuatAng]

efibootmgr has been moved from meta-oe to oe-core but only on master, I've backported these to warrior so that we don't need to depend on meta-oe layer:

http://lists.openembedded.org/pipermail/openembedded-core/2019-August/285489.html

[ChinHuatAng]

@rossburton I was told that the backport will not be accepted for stable branch like warrior, so the getting started guide would have to diverge for master/warrior.