ACPI: EC: Drop ECDT-based boot_ec as soon as we find DSDT-based one.

ASUS notebooks have numerous problems with EC initialization
This patch tries to work around three known issues reported
in bugzilla 8598, 8709 and 8909/8919.

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