armv8: Remove dependency of SERDES for LSCH2 and LSCH3

Remove dependency of SYS_HAS_SERDES for Layerscape Chasis 2 and
Layerscape Chasis 3.

Signed-off-by: Sriram Dash <sriram.dash@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>