MIPS: Octeon: drop dependency on CONFIG_HOLES_IN_ZONE

CAVIUM_OCTEON_SOC configuration selects HOLES_IN_ZONE option to cope with
memory crashes that were happening in 2011.

This option effectively aliases pfn_valid_within() to pfn_valid() when
enabled and hardwires it to 1 when disabled. The check for
pfn_valid_within() is only relevant in case the memory map may have holes
or undefined struct page instances inside MAX_ORDER chunks.

Since 2011 memory management initialization in general and memory map
initialization particularly became much more robust so the check for
pfn_valid_within() is not required on Octeon even despite its, hmm, unusual
memory setup.

Remove the selection of HOLES_IN_ZONE by CAVIUM_OCTEON_SOC and drop the
HOLES_IN_ZONE configuration option entirely as Octeon was the only MIPS
platform to use it.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>