powerpc/ps3: Interrupt code cleanup

General code cleanup for PS3 interrupt.c:

 o Fill out comments for structure members.
 o Move variables ipi_debug_brk_mask and lock from struct ps3_bmp to
   struct ps3_private.
 o Fix pr_debug build errors when DEBUG is defined.
 o Convert bit operation to set_bit().
 o Convert DBG macro from pr_debug to pr_devel
 o Add new macro FAIL to replace pr_debug calls

Signed-off-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>