arm64: alternatives: add enable parameter to conditional asm macros

There are cases where we want to compile out both versions of an
alternative code block, so add an enable parameter to the new conditional
alternative assembly macros in the same way as alternative_insn.
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/alternative.h

@@ -91,11 +91,13 @@ void free_alternatives_memory(void);
  * The code that follows this macro will be assembled and linked as
  * normal. There are no restrictions on this code.
  */
-.macro alternative_if_not cap
+.macro alternative_if_not cap, enable = 1
+	.if \enable
 	.pushsection .altinstructions, "a"
 	altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
 	.popsection
 661:
+	.endif
 .endm
 
 /*
@@ -112,18 +114,22 @@ void free_alternatives_memory(void);
  *    alternative sequence it is defined in (branches into an
  *    alternative sequence are not fixed up).
  */
-.macro alternative_else
+.macro alternative_else, enable = 1
+	.if \enable
 662:	.pushsection .altinstr_replacement, "ax"
 663:
+	.endif
 .endm
 
 /*
  * Complete an alternative code sequence.
  */
-.macro alternative_endif
+.macro alternative_endif, enable = 1
+	.if \enable
 664:	.popsection
 	.org	. - (664b-663b) + (662b-661b)
 	.org	. - (662b-661b) + (664b-663b)
+	.endif
 .endm
 
 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)	\