msm: pm-8x60: Use dma_alloc_coherent for the saved region

dma_alloc_coherent is the linux standard way of allocating coherent
(i.e. uncached) memory. This API provides more guarantess than the
custom allocate_contiguous_ebi function, including the ability to
specify allocations from the lower 4G of memory. Switch to this API
for allocation of uncached memory. Because using dma_alloc_coherent
may have other setup involved, switch the setup function to be a
later initcall as well (from core_initcall to arch_initcall).

Change-Id: I96ea4575e5ee82ccbf7e691ba75ea1414dc6d81a
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>