resource: provide 0args DEFINE_RES variant for unset resource desc

resource: provide 0args DEFINE_RES variant for unset resource desc

Provide a variant of DEFINE_RES that takes 0 arguments to initialize an
"unset" resource descriptor.

This should be used for the improper case of

	struct resource res = {};

where DEFINE_RES() should be used.

With this new helper variant, it would result in:

	struct resource res = DEFINE_RES();

instead of having to define the full 3 arguments:

	struct resource res = DEFINE_RES(0, 0, IORESOURCE_UNSET);

DEFINE_RES() with no args, will set the flags to IORESOURCE_UNSET
signaling the resource descriptor is UNSET and doesn't reflect an actual
resource currently.

Link: https://lkml.kernel.org/r/20251213115314.16700-1-ansuelsmth@gmail.com
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>