PCI: MIPS: use generic pcibios_set_master()

This patch removes MIPS' architecture-specific 'pcibios_set_master()'
routine and lets the default PCI core based implementation handle PCI
device 'latency timer' setup.

No functional change.

Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>