[AVR32] Fix NMI handler

Fix a problem with the NMI handler entry code related to the NMI handler
sharing some code with the exception handlers. This is not a good idea
because the RSR and RAR registers are not the same, and the NMI handler
runs with interrupts masked the whole time so there's no need to check
for pending work.

Open-code the low-level NMI handling logic instead so that the pt_regs
layout is actually correct when the higher-level handler is called.
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

arch/avr32/kernel/entry-avr32b.S

@@ -340,12 +340,34 @@ do_bus_error_read:
 do_nmi_ll:
 	sub	sp, 4
 	stmts	--sp, r0-lr
-	/* FIXME: Make sure RAR_NMI and RSR_NMI are pushed instead of *_EX */
-	rcall	save_full_context_ex
+	mfsr	r9, SYSREG_RSR_NMI
+	mfsr	r8, SYSREG_RAR_NMI
+	bfextu	r0, r9, MODE_SHIFT, 3
+	brne	2f
+
+1:	pushm	r8, r9	/* PC and SR */
 	mfsr	r12, SYSREG_ECR
 	mov	r11, sp
 	rcall	do_nmi
-	rjmp	bad_return
+	popm	r8-r9
+	mtsr	SYSREG_RAR_NMI, r8
+	tst	r0, r0
+	mtsr	SYSREG_RSR_NMI, r9
+	brne	3f
+
+	ldmts	sp++, r0-lr
+	sub	sp, -4		/* skip r12_orig */
+	rete
+
+2:	sub	r10, sp, -(FRAME_SIZE_FULL - REG_LR)
+	stdsp	sp[4], r10	/* replace saved SP */
+	rjmp	1b
+
+3:	popm	lr
+	sub	sp, -4		/* skip sp */
+	popm	r0-r12
+	sub	sp, -4		/* skip r12_orig */
+	rete
 
 handle_address_fault:
 	sub	sp, 4