powerpc/32/kdump: Implement crash_setup_regs() using ppc_save_regs()

This replaces the dummy crash_setup_regs function with full-fledged
crash_setup_regs implementation.  On PPC32 we simply use the new
ppc_save_regs function to dump the registers.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>