picoimx: refine provision

. Use userdata, not data
. Use VENDOR and OS variable
. Set active for each slot, make sure boot from the first slot
. Flash u-boot.imx

Change-Id: I3909242cfc19c0ad103f118139cbf2e5e0008cdc
Signed-off-by: fang hui <hui.fang@freescale.com>
Reviewed-on: http://androidsource.ap.freescale.net/project/572
Reviewed-by: fang hui <hui.fang@nxp.com>
Reviewed-by: Wang Haoran <elven.wang@nxp.com>