ARM: imx5: use dynamic mapping for DPLL block

Replace the static mapping of DPLL block with dynamic mapping by
calling ioremap().  Ideally, this should be done by calling of_iomap(),
so that the physical address of DPLL can also be retrieved from device
tree.  But unfortunately, DPLL blocks are not defined in DT in the first
place.  So to maintain the compatibility of existing DTB, we use
ioremap() with physical address defines in the code.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>