target-i386: Introduce hw_{local,global}_breakpoint_enabled()

target-i386: Introduce hw_{local,global}_breakpoint_enabled()

hw_breakpoint_enabled() returned a bit field indicating whether a local
breakpoint and/or global breakpoint was enabled. Avoid this number magic
by using explicit boolean helper functions hw_local_breakpoint_enabled()
and hw_global_breakpoint_enabled(), to aid readability.

Reuse them for the hw_breakpoint_enabled() implementation and change
its return type to bool.

While at it, fix Coding Style issues (missing braces).

Signed-off-by: liguang <lig.fnst@cn.fujitsu.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>