Blackfin arch: split apart dump_bfin_regs and merge/remove show_regs from...

Blackfin arch: split apart dump_bfin_regs and merge/remove show_regs from process.c, which was largely duplicated

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>