sparc64: fix warnings in cpukit/score/cpu
sparc64: remove sparc64_install_isr_entries and its callers.

sparc64_install_isr_entries function is no longer used. Removing it also
allows to use the default bsppredriverhook for usiii and bspstart for niagara.
sparc64: fix warnings for ofw function calls
sparc64: make local functions static in conscfg
sparc64: use null in empty argument list