[ARM] pxa: remove the unnecessary restoring of MFP registers

MFP registers are saved and restored by the mfp sys_device before all
other platform devices, and it is unnecessary here.

Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>