ACPI: EC: Eliminate acpi_config_boot_ec()

Notice that acpi_ec_add() calls acpi_config_boot_ec() when it finds
that the device object passed to it represents a "boot" EC, but in
that case the ec pointer passed to acpi_config_boot_ec() is guaranteed
to be equal to boot_ec and ec->handle is passed as the handle
argument to it, so acpi_config_boot_ec() really only calls
acpi_ec_setup() and prints a message.

Avoid the pointless checks in acpi_config_boot_ec() by calling
acpi_ec_setup() directly and print the message separately.

With the above changes in place, there are no users of
acpi_config_boot_ec(), so drop it.

No intentional functional impact except for a changed message.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>