ACPI: scan: Use ida_alloc() instead of ida_simple_get()

As recommended in include/linux/idr.h, use ida_alloc() instead of
ida_simple_get() for creating unique device object names and for
symmetry replace ida_simple_remove() with ida_free() (and fix up
the related overly long code line while at it).

Also drop the ACPI_MAX_DEVICE_INSTANCES limit that is not necessary
any more and may not be sufficient for future platforms.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>