m68k: mm: Move initrd phys_to_virt handling after paging_init()

In the Linux kernel, the following vulnerability has been resolved:

m68k: mm: Move initrd phys_to_virt handling after paging_init()

When booting with an initial ramdisk on platforms where physical memory

does not start at address zero (e.g. on Amiga):

initrd: 0ef0602c - 0f800000

Zone ranges:

DMA [mem 0x0000000008000000-0x000000f7ffffffff]

Normal empty

Movable zone start for each node

Early memory node ranges

node 0: [mem 0x0000000008000000-0x000000000f7fffff]

Initmem setup node 0 [mem 0x0000000008000000-0x000000000f7fffff]

Unable to handle kernel access at virtual address (ptrval)

Oops: 00000000

Modules linked in:

PC: [<00201d3c>] memcmp+0x28/0x56

As phys_to_virt() relies on m68k_memoffset and module_fixup(), it must

not be called before paging_init(). Hence postpone the phys_to_virt

handling for the initial ramdisk until after calling paging_init().

While at it, reduce #ifdef clutter by using IS_ENABLED() instead.