ls1021aqds: add hwconfig setting to do pin mux

The Freescale LS1021AQDS share some pins, so Add the hwconfig option
that allows the user to choose which the function he wants.

The main pin mux IP is:
eSDHC, SAI, IIC2, RGMII, CAN, SAI.

Signed-off-by: Yuan Yao <yao.yuan@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>