docs(layerscape): add ls1046a soc and board support

Update document for nxp-layerscape to add ls1046a SoC and ls1046ardb,
ls1046afrwy board support.

Also update maintainer of ls1046a platforms.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>
Change-Id: I522f978bc93aa8d1f1d60fa8efef392b7d854df7
2 files changed