ACPI: Introduce has_acpi_companion()

Now that the ACPI companions of devices are represented by pointers
to struct fwnode_handle, it is not quite efficient to check whether
or not an ACPI companion of a device is present by evaluating the
ACPI_COMPANION() macro.

For this reason, introduce a special static inline routine for that,
has_acpi_companion(), and update the code to use it where applicable.

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