linuxkpi: Define __GFP_THISNODE
It is used to force the NUMA node to allocate from. This flag is
unimplemented for now because we don't have an implementation of
alloc_pages_node() yet.
The DRM TTM code started to use this flag in Linux 6.12.
Reviewed by: bz
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D56436