ACPI: EC: Enable boot EC before bus_scan

Some _STA methods called during bus_scan() might require EC region handler,
which might be enabled later in the scan.
Enable it explicitly before scan to avoid errors.

Reference: http://bugzilla.kernel.org/show_bug.cgi?id=9627

Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>