sparc64: kdump: set crashing_cpu for panic

sparc64: kdump: set crashing_cpu for panic

crashing_cpu was only being set in die_if_kernel() but not when a
crash dump is initiated from panic(). Move the initialization to
machine_crash_shutdown().

Also call bust_spinlocks() from die_if_kernel() to get rid of a warning
in smp_call_function_many(). It's already called in the panic path.

Orabug: 23585248

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
(cherry picked from commit 1b588be700fac73edd07c015ff53aecba5d92bec)
Signed-off-by: Allen Pais <allen.pais@oracle.com>