Revert "intel: Remove unneded pthread mutex in LOCK_HARDWARE."

Revert "intel: Remove unneded pthread mutex in LOCK_HARDWARE."

This reverts commit de447afff26706e3bf8bdcd5cfb8b1daf49b4b21 but
puts the lock under DRI1-only.

From keithw:
> It's there because the DRI1 code doesn't actually achieve the mutexing
> which it looks as if it should.  For multi-threaded applications it was
> always possible to get two threads inside locked regions -- I have no
> idea how, but it certainly was and presumably still is possible.