ARM: dts: ls1021a: fix flextimer failed to wake system

The data of property 'fsl,rcpm-wakeup' is not corrcet, which causing
RCPM driver incorrectly program register IPPDEXPCR1, then flextimer is
wrongly clock gated during system suspend, can't send interrupt to
wake.

Signed-off-by: Ran Wang <ran.wang_1@nxp.com>
Acked-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>