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/lantiq/irq.c

@@ -61,7 +61,7 @@
 /* we have a cascade of 8 irqs */
 #define MIPS_CPU_IRQ_CASCADE		8
 
-#if defined(CONFIG_MIPS_MT_SMP) || defined(CONFIG_MIPS_MT_SMTC)
+#ifdef CONFIG_MIPS_MT_SMP
 int gic_present;
 #endif
 
@@ -440,7 +440,7 @@ int __init icu_of_init(struct device_node *node, struct device_node *parent)
 	arch_init_ipiirq(MIPS_CPU_IRQ_BASE + MIPS_CPU_IPI_CALL_IRQ, &irq_call);
 #endif
 
-#if !defined(CONFIG_MIPS_MT_SMP) && !defined(CONFIG_MIPS_MT_SMTC)
+#ifndef CONFIG_MIPS_MT_SMP
 	set_c0_status(IE_IRQ0 | IE_IRQ1 | IE_IRQ2 |
 		IE_IRQ3 | IE_IRQ4 | IE_IRQ5);
 #else