Correctly specify treeboot based image entrypoint.  Currently makefile uses
$(ENTRYPOINT) which isn't defined anywhere.  Each board port sets
entrypoint-$(CONFIG_BOARD_NAME) instead.

Without this patch I cannot boot Ocotea (PPC440GX eval board) anymore.  I
was getting random "OS panic" errors from OpenBIOS for a while, but with
current kernel I get them all the time (probably because image became
bigger).
Signed-off-by: NEugene Surovegin <ebs@ebshome.net>
Acked-by: NTom Rini <trini@kernel.crashing.org>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>