MAINTAINERS: Update locking tree description and file patterns

Update the file patterns, the Git tree URI and also widen the
scope from 'LOCKDEP and LOCKSTAT' to 'LOCKING PRIMITIVES'.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org