ARM: 8421/1: smp: Collapse arch_cpu_idle_dead() into cpu_die()

The only caller of cpu_die() on ARM is arch_cpu_idle_dead(), so
let's simplify the code by renaming cpu_die() to
arch_cpu_idle_dead(). While were here, drop the __ref annotation
because __cpuinit is gone nowadays.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>