HW-BKPT: Introduce new features to the hw-breakpoint infrastructure - ver II

Hi All,
Please find a set of patches that implement the features listed
below, the previous version of which was posted here:
http://lkml.org/lkml/2009/8/26/477

Patch 1/2: Allow per-cpu kernel-space Hardware Breakpoint requests Patch 2/2: Allow kernel breakpoints to be modified through a new API Patch 3/3: Allow breakpoints to be enabled/disabled without yielding the breakpoint request through a new API - enable_hw_breakpoint().

Changelog ver II
-----------------
- Fixed a potential race between updation of per-cpu kernel-space breakpoint structures and a concurrent breakpoint exception by disabling breakpoints in remove_each_cpu_kernel_hbp() through a new function arch_disable_hw_breakpoint().
- Change the data-type of 'enabled' member in 'struct hw_breakpoint' to 'bool'.
- Split the enable_hw_breakpoint() interface to bring a counterpart in disable_hw_breakpoint().
- Modify stale/incorrect comments.
- Code updated to commit 1468c4ea3af77ac75de7aae80a44522ff5d0d6c5 of -tip tree.

Thanks,
K.Prasad