platform/x86: wmi: Remove custom EC address space handler

The custom EC address space handler in the WMI driver was only needed
because the EC driver did not install its address space handler for
EC operation regions beyond the EC device scope in the ACPI namespace.

That has just changed, so the custom EC address handler is not needed
any more and it can be removed.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>