ARM: Remove __ref on hotplug cpu die path

Now that __cpuinit has been removed, the __ref markings on these
functions are useless. Remove them. This also reduces the size of
the multi_v7_defconfig image:

$ size before after
   text    data     bss     dec     hex filename
   12683578        1470996  348904 14503478         dd4e36 before
   12683274        1470996  348904 14503174         dd4d06 after

presumably because now we don't have to jump to code in the
.ref.text section and/or the noinline marking is removed.

Cc: Shiraz Hashim <shiraz.linux.kernel@gmail.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: <linux-omap@vger.kernel.org>
Cc: <linux-arm-msm@vger.kernel.org>
Cc: <spear-devel@list.st.com>
Cc: <linux-tegra@vger.kernel.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Barry Song <baohua@kernel.org>
Acked-by: Andy Gross <agross@codeaurora.org>
Acked-by: Viresh Kumar <vireshk@kernel.org>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Olof Johansson <olof@lixom.net>