platform/x86: simatic-ipc: drop custom P2SB bar code

The two drivers that used to use this have been switched over to the
common P2SB accessor, so this code is not needed any longer.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Lee Jones <lee@kernel.org>