docs(plat/nxp/layerscape): add ls1043a soc and board support

Update document for nxp-layerscape to add ls1043a SoC and ls1043ardb
board support.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>
Change-Id: I8442daf08a0f7c1ba982a3ed1d0ad24c4c420185
1 file changed