ARM: EXYNOS: Move code from hotplug.c to platsmp.c

Cleanup a little the SMP/hotplug code for Exynos by:
1. Moving completely all functions from hotplug.c into the platsmp.c;
2. Deleting the hotplug.c file.

After recent cleanups (e.g. 75ad2ab2

 "ARM: EXYNOS: use
v7_exit_coherency_flush macro for cache disabling") there was only CPU
power down related code in hotplug.c file.

Rationale behind the code movement and benefits:
1. The file platsmp.c is the only user of code located in hotplug.c.
   Keeping code in hotplug.c required declaring exynos_cpu_die() in common.h.
   Such dependencies and mentioned exynos_cpu_die() declaration can be
   removed.
2. In next patches exynos_set_delayed_reset_assertion() will be
   introduced. This function will be called by:
    - cpu_leave_power (hotplug.c),
    - platform_do_lowpower (hotplug.c),
    - exynos_boot_secondary (platsmp.c).

Merging hotplug.c into platsmp.c leads to simpler and cleaner code with
less dependencies between files.

The commit only moves code around with one additional observable change:
the hotplug.c was compiled with custom CFLAGS (-march=armv7-a). These
CFLAGS are not necessary any more.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>