ACPI / x86: boot: Get rid of ACPI_INVALID_GSI

Commit 49e4b843 (ACPI: Use correct IRQ when uninstalling ACPI
interrupt handler) brings a new definition for invalid ACPI IRQ,
i.e. INVALID_ACPI_IRQ, which is defined to 0xffffffff (or -1 for
unsigned value).

Get rid of a former one, which was brought in by commit 2c0a6894
(x86, ACPI, irq: Enhance error handling in function acpi_register_gsi()),
in favour of latter.

To clarify the rationale of changing from INT_MIN to ((unsigned)-1)
definition consider the following:
- IRQ 0 is valid one in hardware, so, better not to use it everywhere
  (Linux uses 0 as NO IRQ, though it's another story)
- INT_MIN splits the range into two, while 0xffffffff reserves only the
  last item
- when type casting is done in most cases 0xff, 0xffff is naturally used
  as a marker of invalid HW IRQ: for example PCI INT line 0xff means
  no IRQ assigned by BIOS

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