ARM: imx5: move init hooks into mach-imx5x.c

These imx5 init_early[late] hooks are called only from mach-imx5x.c.
Let's move them into mach-imx5x.c.

While at it, replace the static mapping in imx51_ipu_mipi_setup() with
dynamic mapping.  Also this function and imx_src_init() do not
necessarily to be called at .init_early hook, so move them into
.init_machine.

The mxc_iomux_v3_init() is dropped from imx51_init_early() in the
moving, since it's only needed by non-DT boot.

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