LU-11986 libcfs: provide QSTR_INIT compat macro

LU-11986 libcfs: provide QSTR_INIT compat macro

Provide a compat macro for QSTR_INIT() for older kernels.

Fixes: 9d42660e173e ("LU-11986 lnet: properly cleanup lnet debugfs files")
Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ice19a4dad8456551ba398034a8d3942068006512
Reviewed-on: https://review.whamcloud.com/38090
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>