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/include/asm/mips_mt.h

@@ -1,7 +1,6 @@
 /*
- * Definitions and decalrations for MIPS MT support
- * that are common between SMTC, VSMP, and/or AP/SP
- * kernel models.
+ * Definitions and decalrations for MIPS MT support that are common between
+ * the VSMP, and AP/SP kernel models.
  */
 #ifndef __ASM_MIPS_MT_H
 #define __ASM_MIPS_MT_H