Based upon a report and initial patch by Friedrich Oslage.

The intention is to provide this facility for
__trigger_all_cpu_backtrace even if MAGIC_SYSRQ is not set.

The only part that should have MAGIC_SYSRQ ifdef protection is the
sparc_globalreg_op sysrq regitration and immediate code.
Signed-off-by: David S. Miller <davem@davemloft.net>