LAM enabling is only allowed when the process has single thread.
LAM mode is inherited into child thread.

Trying to enable LAM after spawning a thread has to fail.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20230312112612.31869-18-kirill.shutemov%40linux.intel.com