ARM: EXYNOS: add coupled cpuidle support for Exynos3250

The following patch adds coupled cpuidle support for Exynos3250 to
an existing cpuidle-exynos driver.  As a result it enables AFTR mode
to be used by default on Exynos3250 without the need to hot unplug
CPU1 first.

The detailed changelog:
- use exynos_[get,set]_boot_addr() in cpuidle-exynos.c and then make
  cpu_boot_reg_base() static
- use exynos_core_restart() in exynos_cpu0_enter_aftr()
- add missing smp_rmb() to exynos_cpu0_enter_aftr() (to make the code
  in-sync with the platform SMP code)
- add call_firmware_op(cpu_boot, 1) to exynos_cpu0_enter_aftr()
- use dsb_sev() instead of IPI wakeup for Exynos3250 in
  exynos_cpu0_enter_aftr()
- add CPU0 vs CPU1 synchronization based on S5P_PMU_SPARE2 register
  for Exynos3250 to cpuidle-exynos.c
- add flush_cache_all() for CPU1/0 before powerdown/AFTR for
  Exynos3250 to exynos_wfi_finisher()/exynos_do_idle()

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>