btrfs: disable allocation warnings for compression workspaces

The workspaces for compression are typically much larger than a page and
for high zstd levels in the range of megabytes. There's a fallback to
vmalloc but this can still fail (see the report).

Some of the workspaces are preallocated at module load time so we have a
safe fallback, otherwise when a new workspace is needed it's allocated
but if this fails then the process waits. Which means the warning is
only causing noise and we can use the GFP flag to disable it.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=217466
Signed-off-by: David Sterba <dsterba@suse.com>