MIPS: Make local_irq_disable macro safe for non-Mipsr2

For non-mipsr2 processors, the local_irq_disable contains an mfc0-mtc0
pair with instructions inbetween.  With preemption enabled, this sequence
may get preempted and effect a stale value of CP0_STATUS when executing
the mtc0 instruction.  This commit avoids this scenario by incrementing
the preempt count before the mfc0 and decrementing it after the mtc9.

[ralf@linux-mips.org: This patch is sorting out the part that were missed
by e97c5b60

 [MIPS: Make irqflags.h functions preempt-safe for non-mipsr2
cpus.]  I also re-enabled the inclusion of <asm/asm-offsets.h> at the top
of <asm/asmmacro.h>].

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: cernekee@gmail.com
Patchwork: https://patchwork.linux-mips.org/patch/6164/


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