dma: iproc_pax_v2: delay initialization after pcie

The Broadcom pcie setup has a devicetree dependency like:

/pcie/paxdma -> /pcie/pcie -> /soc/pl330

Add a separate init symbol for iproc_pax_v2 so that these gets
initialized in order, fixes this error:

$ west build -p -b bcm958402m2_m7 tests/kernel/common \
	-DCONFIG_CHECK_INIT_PRIORITIES=y
...
ERROR: /pcie/paxdma@4e100800 POST_KERNEL 40 < \
	/pcie/pcie@4e100000 POST_KERNEL 50

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>