update p4a kernel

merge from p4a-kernel.git : commit 90429fda66b5166eb02b5ee7d859a3ec909a0091
update p4a building configurations

divide p4a into two subtarget : standalone and dual,
	   "standalone" means P4A CPU2-only run mode, and
	   "dual" means P4A CPU2 & CPU1 run mode.