LU-9859 libcfs: migrate libcfs_mem.c to lnet/lib-mem.c

LU-9859 libcfs: migrate libcfs_mem.c to lnet/lib-mem.c

Move the libcfs_mem.c code to the LNet core. The prototypes are declared in libcfs_cpu.h
but we don't move them yet since the CPT code depends on the libcfs_mem.c work. This can
end up in a modular cyclic dependency if we move the CPT work right away so limit what is
changed at this point.

Test-Parameters: trivial
Change-Id: I6bf5cd9f20033f988dde1989f0fc5f89ea74b5a2
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52701
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>