[POWERPC] QE: implement qe_muram_offset

qe_muram_offset is the reverse of the qe_muram_addr, will be
used for the Freescale QE USB Host Controller driver.

This patch also moves qe_muram_addr into the qe.h header, plus
adds __iomem hints to use with sparse.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>