Disable elision for lglock readers

lglocks reader locks very rarely have any contention, because they
are normally only used privately on each CPU.

Don't run them with elision. The risk of aborting for some reason
outweights the benefit of eliding them. This helps in particular
the dcache, which has a tendency to exceed the transaction
capacity of Haswell during dcache walks.

Signed-off-by: Andi Kleen <ak@linux.intel.com>