ARM: hw_breakpoint: don't clear bkpts during halting mode debug

Skip clearing breakpoints and enabling monitor mode when halting
debug mode is enabled. This avoids wiping out user configured
breakpoints as part of halting mode debug.

Change-Id: I0dcd1b7dc048f3d795b0c7c31ba6b90d7b6e9eeb
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>