powerpc/mem: Move CMA reservations to arch_mm_preinit

powerpc/mem: Move CMA reservations to arch_mm_preinit

commit 4267739cabb8 ("arch, mm: consolidate initialization of SPARSE memory model"),
changed the initialization order of "pageblock_order" from...
start_kernel()
    - setup_arch()
       - initmem_init()
         - sparse_init()
           - set_pageblock_order();  // this sets the pageblock_order
       - xxx_cma_reserve();

to...
start_kernel()
    - setup_arch()
       - xxx_cma_reserve();
    - mm_core_init_early()
       - free_area_init()
          - sparse_init()
             - set_pageblock_order() // this sets the pageblock_order.

So this means, pageblock_order is not initialized before these cma
reservation function calls, hence we are seeing CMA failures like...

[    0.000000] kvm_cma_reserve: reserving 3276 MiB for global area
[    0.000000] cma: pageblock_order not yet initialized. Called during early boot?
[    0.000000] cma: Failed to reserve 3276 MiB
....
[    0.000000][    T0] cma: pageblock_order not yet initialized. Called during early boot?
[    0.000000][    T0] cma: Failed to reserve 1024 MiB

This patch moves these CMA reservations to arch_mm_preinit() which
happens in mm_core_init() (which happens after pageblock_order is
initialized), but before the memblock moves the free memory to buddy.

Fixes: 4267739cabb8 ("arch, mm: consolidate initialization of SPARSE memory model")
Suggested-by: Mike Rapoport <rppt@kernel.org>
Reported-and-tested-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Closes: https://lore.kernel.org/linuxppc-dev/4c338a29-d190-44f3-8874-6cfa0a031f0b@linux.ibm.com/
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Tested-by: Dan Horák <dan@danny.cz>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/6e532cf0db5be99afbe20eed699163d5e86cd71f.1772303986.git.ritesh.list@gmail.com