MIPS: Oprofile: Loongson: Cleanup of the macros

The _EXL, _KERNEL etc. bits are in the performance control register so
use _PERFCTRL prefix instead of _PERFCNT.  While at it make the macro
more readable, use _ENABLE instead of _INT_EN suffix to describe the
interrupt enable bit.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/1203/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>