powerpc/85xx: Add support usb2/etsec and tdm/audio pin multiplex on P1022DS

powerpc/85xx: Add support usb2/etsec and tdm/audio pin multiplex on P1022DS

For soc which have pin multiplex relation, some of them can't enable
simultaneously. This patch add environment var 'hwconfig' content
defination for them. you can enable some one function by setting
environment var 'hwconfig' content and reset board. Detail setting
please refer doc/README.p1022ds

Signed-off-by: Jiang Yutang <b14898@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>