meta-inspur: update Yocto compat for gatesgarth

Since the current release of Yocto is gatesgarth, Add and support for
gatesgarth(current) and dunsfell(previous) in meta-inspur layer.

Also, remove the two earlier releases(warrior and zeus).

Tested: Built successfully on fp5280g2 and on5263m5.

(From meta-inspur rev: 831b68cce11da461122ee20ad371d93b60a245b1)

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I587a032a20bb645c452d16fbdc8adff3d35c965a
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>