LU-14289 ptlrpc: move heap.c from libcfs to ptlrpc

LU-14289 ptlrpc: move heap.c from libcfs to ptlrpc

cfs_binheap is only used by the nrs code in ptlrpc, so move it out of
libcfs to the one place it is used.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I4687d4de0a83e0ce106d4f4cfd5ea95faef27dfc
Reviewed-on: https://review.whamcloud.com/41129
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>