MIPS: MT: Remove SMTC support

Nobody is maintaining SMTC anymore and there also seems to be no userbase.
Which is a pity - the SMTC technology primarily developed by Kevin D.
Kissell <kevink@paralogos.com> is an ingenious demonstration for the MT
ASE's power and elegance.

Based on Markos Chandras <Markos.Chandras@imgtec.com> patch
https://patchwork.linux-mips.org/patch/6719/ which while very similar did
no longer apply cleanly when I tried to merge it plus some additional
post-SMTC cleanup - SMTC was a feature as tricky to remove as it was to
merge once upon a time.

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

arch/mips/kernel/entry.S

@@ -16,9 +16,6 @@
 #include <asm/isadep.h>
 #include <asm/thread_info.h>
 #include <asm/war.h>
-#ifdef CONFIG_MIPS_MT_SMTC
-#include <asm/mipsmtregs.h>
-#endif
 
 #ifndef CONFIG_PREEMPT
 #define resume_kernel	restore_all
@@ -89,41 +86,6 @@ FEXPORT(syscall_exit)
 	bnez	t0, syscall_exit_work
 
 restore_all:				# restore full frame
-#ifdef CONFIG_MIPS_MT_SMTC
-#ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP
-/* Re-arm any temporarily masked interrupts not explicitly "acked" */
-	mfc0	v0, CP0_TCSTATUS
-	ori	v1, v0, TCSTATUS_IXMT
-	mtc0	v1, CP0_TCSTATUS
-	andi	v0, TCSTATUS_IXMT
-	_ehb
-	mfc0	t0, CP0_TCCONTEXT
-	DMT	9				# dmt t1
-	jal	mips_ihb
-	mfc0	t2, CP0_STATUS
-	andi	t3, t0, 0xff00
-	or	t2, t2, t3
-	mtc0	t2, CP0_STATUS
-	_ehb
-	andi	t1, t1, VPECONTROL_TE
-	beqz	t1, 1f
-	EMT
-1:
-	mfc0	v1, CP0_TCSTATUS
-	/* We set IXMT above, XOR should clear it here */
-	xori	v1, v1, TCSTATUS_IXMT
-	or	v1, v0, v1
-	mtc0	v1, CP0_TCSTATUS
-	_ehb
-	xor	t0, t0, t3
-	mtc0	t0, CP0_TCCONTEXT
-#endif /* CONFIG_MIPS_MT_SMTC_IM_BACKSTOP */
-/* Detect and execute deferred IPI "interrupts" */
-	LONG_L	s0, TI_REGS($28)
-	LONG_S	sp, TI_REGS($28)
-	jal	deferred_smtc_ipi
-	LONG_S	s0, TI_REGS($28)
-#endif /* CONFIG_MIPS_MT_SMTC */
 	.set	noat
 	RESTORE_TEMP
 	RESTORE_AT