[MIPS] Sibyte: Fix ZBbus profiler

[MIPS] Sibyte: Fix ZBbus profiler

 o Fix build error.
 o Handle error returns.
 o Deal with signals received while sleeping.
 o Don't allow to be selected when we're not building the directory with
   the driver anyway.
 o Coding style cleanups.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>