MIPS: Fix protected_cache(e)_op() for microMIPS

When building for microMIPS we need to ensure that the assembler always
knows that there is code at the target of a branch or jump. Commit
7170bdc77755 ("MIPS: Add return errors to protected cache ops")
introduced a fixup path to protected_cache(e)_op() which does not meet
this requirement. The fixup path jumps to the "2" label but the .section
pseudo-op immediately following it causes the label to be marked as
data. Linking then fails with:

mips-img-linux-gnu-ld: arch/mips/mm/c-r4k.o: .fixup+0x0: Unsupported
jump between ISA modes; consider recompiling with interlinking
enabled.

Fix this by declaring that "2" labels code using the .insn directive.

Fixes: 7170bdc77755 ("MIPS: Add return errors to protected cache ops")
Signed-off-by: Paul Burton <[e-mail]>
Signed-off-by: James Hogan <[e-mail]>
Reviewed-by: Maciej W. Rozycki <[e-mail]>
Cc: [e-mail]
Cc: Ralf Baechle <[e-mail]>
Patchwork: https://patchwork.linux-mips.org/patch/15274/
Signed-off-by: James Hogan <[e-mail]>

arch/mips/include/asm/r4kcache.h

···
 	"	.set	noreorder		\n"		\
 	"	.set "MIPS_ISA_ARCH_LEVEL"	\n"		\
 	"1:	cache	%1, (%2)		\n"		\
-	"2:	.set	pop			\n"		\
+	"2:	.insn				\n"		\
+	"	.set	pop			\n"		\
 	"	.section .fixup,\"ax\"		\n"		\
 	"3:	li	%0, %3			\n"		\
 	"	j	2b			\n"		\
···
 	"	.set	mips0			\n"		\
 	"	.set	eva			\n"		\
 	"1:	cachee	%1, (%2)		\n"		\
-	"2:	.set	pop			\n"		\
+	"2:	.insn				\n"		\
+	"	.set	pop			\n"		\
 	"	.section .fixup,\"ax\"		\n"		\
 	"3:	li	%0, %3			\n"		\
 	"	j	2b			\n"		\