intel/agp: rewrite GTT on resume

On my Intel chipset (965GM), the GTT is entirely erased across
suspend/resume.  This patch simply re-plays the current mapping at resume
time to restore the table.=20

I noticed this once I started relying on persistent GTT mappings across VT
switch in our GEM work -- the old X server and DRM code carefully unbind
all memory from the GTT on VT switch, but GEM does not bother.

I placed the list management and rewrite code in the generic layer on the
assumption that it will be needed on other hardware, but I did not add the
rewrite call to anything other than the Intel resume function.

Keep a list of current GATT mappings.  At resume time, rewrite them into
the GATT.  This is needed on Intel (at least) as the entire GATT is
cleared across suspend/resume.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Keith Packard <keithp@keithp.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/char/agp/backend.c

@@ -185,6 +185,8 @@ static int agp_backend_initialize(struct agp_bridge_data *bridge)
 		rc = -EINVAL;
 		goto err_out;
 	}
+	INIT_LIST_HEAD(&bridge->mapped_list);
+	spin_lock_init(&bridge->mapped_lock);
 
 	return 0;