powerpc/mm: don't display empty early ioremap area

On the 8xx, the layout displayed at boot is:

[    0.000000] Memory: 121856K/131072K available (5728K kernel code, 592K rwdata, 1248K rodata, 560K init, 448K bss, 9216K reserved, 0K cma-reserved)
[    0.000000] Kernel virtual memory layout:
[    0.000000]   * 0xffefc000..0xffffc000  : fixmap
[    0.000000]   * 0xffefc000..0xffefc000  : early ioremap
[    0.000000]   * 0xc9000000..0xffefc000  : vmalloc & ioremap
[    0.000000] SLUB: HWalign=16, Order=0-3, MinObjects=0, CPUs=1, Nodes=1

Remove display of an empty early ioremap.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f6267226038cb25a839b567319e240576e3f8565.1565793287.git.christophe.leroy@c-s.fr