sparc64: Don't MAGIC_SYSRQ ifdef smp_fetch_global_regs and support code.

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>