The following mechanisms are OSPM specific:
1. Redirect output destination to console: no file redirection will be
   needed by an in-kernel debugger, there is even no file can be accessed
   when the debugger is running in the kernel mode.
2. Output command prompts: programs other than acpiexec can have different
   prompt characters and the prompt characters may be implemented as a
   special character sequence to form a char device IO protocol.
3. Command ready/complete handshake: OSPM debugger may wait more conditions
   to implement OSPM specific semantics (for example, FIFO full/empty
   conditions for O_NONBLOCK or IO open/close conditions).
Leaving such OSPM specific stuffs in the ACPICA debugger core blocks
Linux debugger IO driver implementation.

Several new OSL APIs are provided by this patch:
1. acpi_os_initialize_command_signals: initialize command handshake mechanism
   or any other OSPM specific stuffs.
2. acpi_os_terminate_command_signals: reversal of
   acpi_os_initialize_command_signals.
3. acpi_os_wait_command_ready: putting debugger task into wait state when a
   command is not ready. OSPMs can terminate command loop by returning
   AE_CTRL_TERMINATE from this API. Normally, wait_event() or
   wait_for_multiple_object() may be used to implement this API.
4. acpi_os_notify_command_complete: putting user task into running state when a
   command has been completed. OSPMs can terminate command loop by
   returning AE_CTRL_TERMINATE from this API. Normally, wake_up() or
   set_event() may be used to implement this API.
This patch also converts current command signaling implementation into a
generic debugger layer (osgendbg.c) to be used by the existing OSPMs or
acpiexec, in return, Linux can have chance to implement its own command
handshake mechanism. This patch also implements acpiexec batch mode in a
multi-threading mode comaptible style as a demo (this can be confirmed by
configuring acpiexec into DEBUGGER_MULTI_THREADED mode where the batch mode
is still working). Lv Zheng.

Note that the OSPM specific command handshake mechanism is required by
Linux kernel because:
1. Linux kernel trends to use wait queue to synchronize two threads, using
   mutexes to achieve that will cause false "dead lock" warnings.
2. The command handshake mechanism implemented by ACPICA is implemented in
   this way because of a design issue in debugger IO streaming. Debugger IO
   outputs are simply cached using a giant buffer, this should be tuned by
   Linux in the future.
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>