ARM: add machine name to stack dump output

The generic dump_stack() code provides the facility to include the
machine name in the stack dump, which can be useful information.  Add
a call to dump_stack_set_arch_desc() for the generic code to print
this information.

Tested-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>