arm64: assembler: remove smp_dmb macro

These days arm64 kernels are always SMP, and thus smp_dmb is an
overly-long way of writing dmb. Naturally, no-one uses it.

Remove the unused macro.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/assembler.h

@@ -79,13 +79,6 @@
 9990:
 	.endm
 
-/*
- * SMP data memory barrier
- */
-	.macro	smp_dmb, opt
-	dmb	\opt
-	.endm
-
 /*
  * RAS Error Synchronization barrier
  */