ARM: Add interface for registering and calling firmware-specific operations

Some boards are running with secure firmware running in TrustZone secure
world, which changes the way some things have to be initialized.

This patch adds an interface for platforms to specify available firmware
operations and call them.

A wrapper macro, call_firmware_op(), checks if the operation is provided
and calls it if so, otherwise returns -ENOSYS to allow fallback to
legacy operation..

By default no operations are provided.

Example of use:

In code using firmware ops:

  __raw_writel(virt_to_phys(exynos4_secondary_startup),
               CPU1_BOOT_REG);

  /* Call Exynos specific smc call */
  if (call_firmware_op(cpu_boot, cpu) == -ENOSYS)
          cpu_boot_legacy(...); /* Try legacy way */

  gic_raise_softirq(cpumask_of(cpu), 1);

In board-/platform-specific code:

  static int platformX_do_idle(void)
  {
          /* tell platformX firmware to enter idle */
          return 0;
  }

  static int platformX_cpu_boot(int i)
  {
          /* tell platformX firmware to boot CPU i */
          return 0;
  }

  static const struct firmware_ops platformX_firmware_ops = {
          .do_idle      = exynos_do_idle,
          .cpu_boot     = exynos_cpu_boot,
          /* other operations not available on platformX */
  };

  static void __init board_init_early(void)
  {
          register_firmware_ops(&platformX_firmware_ops);
  }

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>