x86/hw-breakpoints: Don't lose GE flag while disabling a breakpoint

When we schedule out a breakpoint from the cpu, we also
incidentally remove the "Global exact breakpoint" flag from the
breakpoint control register. It makes us losing the fine grained
precision about the origin of the instructions that may trigger
breakpoint exceptions for the other breakpoints running in this
cpu.

Reported-by: Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1259211878-6013-1-git-send-regression-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>