sh: Fix up DSP context save/restore.

There were a number of issues with the DSP context save/restore code,
mostly left-over relics from when it was introduced on SH3-DSP with
little follow-up testing, resulting in things like task_pt_dspregs()
referencing incorrect state on the stack.

This follows the MIPS convention of tracking the DSP state in the
thread_struct and handling the state save/restore in switch_to() and
finish_arch_switch() respectively. The regset interface is also updated,
which allows us to finally be rid of task_pt_dspregs() and the special
cased task_pt_regs().

Signed-off-by: Michael Trimarchi <michael@evidence.eu.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/processor_32.h

@@ -57,6 +57,14 @@ asmlinkage void __init sh_cpu_init(void);
 #define SR_IMASK	0x000000f0
 #define SR_FD		0x00008000
 
+/*
+ * DSP structure and data
+ */
+struct sh_dsp_struct {
+	unsigned long dsp_regs[14];
+	long status;
+};
+
 /*
  * FPU structure and data
  */
@@ -96,6 +104,11 @@ struct thread_struct {
 
 	/* floating point info */
 	union sh_fpu_union fpu;
+
+#ifdef CONFIG_SH_DSP
+	/* Dsp status information */
+	struct sh_dsp_struct dsp_status;
+#endif
 };
 
 /* Count of active tasks with UBC settings */