MIPS: Add inline asm encoding helpers

To allow simplification of macros which use inline assembly to
explicitly encode instructions, add a few simple abstractions to
mipsregs.h which expand to specific microMIPS or normal MIPS encodings
depending on what type of kernel is being built:

_ASM_INSN_IF_MIPS(_enc) : Emit a 32bit MIPS instruction if microMIPS is
                          not enabled.
_ASM_INSN32_IF_MM(_enc) : Emit a 32bit microMIPS instruction if enabled.
_ASM_INSN16_IF_MM(_enc) : Emit a 16bit microMIPS instruction if enabled.

The macros can be used one after another since the MIPS / microMIPS
macros are mutually exclusive, for example:

__asm__ __volatile__(
        ".set push\n\t"
        ".set noat\n\t"
        "# mfgc0 $1, $%1, %2\n\t"
        _ASM_INSN_IF_MIPS(0x40610000 | %1 << 11 | %2)
        _ASM_INSN32_IF_MM(0x002004fc | %1 << 16 | %2 << 11)
        "move %0, $1\n\t"
        ".set pop"
        : "=r" (__res)
        : "i" (source), "i" (sel));

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13310/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/mipsregs.h

@@ -1048,6 +1048,33 @@ static inline int mm_insn_16bit(u16 insn)
 	return (opcode >= 1 && opcode <= 3) ? 1 : 0;
 }
 
+/*
+ * Helper macros for generating raw instruction encodings in inline asm.
+ */
+#ifdef CONFIG_CPU_MICROMIPS
+#define _ASM_INSN16_IF_MM(_enc)			\
+	".insn\n\t"				\
+	".hword (" #_enc ")\n\t"
+#define _ASM_INSN32_IF_MM(_enc)			\
+	".insn\n\t"				\
+	".hword ((" #_enc ") >> 16)\n\t"	\
+	".hword ((" #_enc ") & 0xffff)\n\t"
+#else
+#define _ASM_INSN_IF_MIPS(_enc)			\
+	".insn\n\t"				\
+	".word (" #_enc ")\n\t"
+#endif
+
+#ifndef _ASM_INSN16_IF_MM
+#define _ASM_INSN16_IF_MM(_enc)
+#endif
+#ifndef _ASM_INSN32_IF_MM
+#define _ASM_INSN32_IF_MM(_enc)
+#endif
+#ifndef _ASM_INSN_IF_MIPS
+#define _ASM_INSN_IF_MIPS(_enc)
+#endif
+
 /*
  * TLB Invalidate Flush
  */