ion: msm: Move msm_ion probe to subsys_initcall_sync

Move MSM ION to subsys_initcall_sync, so that the ION
heaps can be instantiated earlier than what they currently
are when all the drivers are builtin. This will reduce
the number of probe retrials that can occur if clients
attempt to use the MSM ION APIs before the MSM ION driver
has probed.

Change-Id: Ic308cb243541e0b1985544f1993eb83926452520
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>