sh: Tidy up ELF core dumps.

These have been using overrides for ELF_CORE_COPY_TASK_REGS and
ELF_CORE_COPY_FPREGS while the generic versions can be used instead.
Presently the pt_regs are also duplicated across elf_core_copy_regs()
and elf_core_copy_task_regs(), this switches to simply copying out
through elf_core_copy_regs() instead.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>