CVE-2023-54167

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

m68k: mm: Move initrd phystovirt 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 phystovirt() relies on m68kmemoffset and modulefixup(), it must not be called before paginginit(). Hence postpone the phystovirt handling for the initial ramdisk until after calling paginginit().

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