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/pmcs-msp71xx/msp_irq_per.c

@@ -113,9 +113,6 @@ void __init msp_per_irq_init(void)
 	/* initialize all the IRQ descriptors */
 	for (i = MSP_PER_INTBASE; i < MSP_PER_INTBASE + 32; i++) {
 		irq_set_chip(i, &msp_per_irq_controller);
-#ifdef CONFIG_MIPS_MT_SMTC
-		irq_hwmask[i] = C_IRQ4;
-#endif
 	}
 }