FROMLIST: arm64: fix alternatives with LLVM's integrated assembler

LLVM's integrated assembler fails with the following error when
building KVM:

  <inline asm>:12:6: error: expected absolute expression
   .if kvm_update_va_mask == 0
       ^
  <inline asm>:21:6: error: expected absolute expression
   .if kvm_update_va_mask == 0
       ^
  <inline asm>:24:2: error: unrecognized instruction mnemonic
          NOT_AN_INSTRUCTION
          ^
  LLVM ERROR: Error parsing inline asm

These errors come from ALTERNATIVE_CB and __ALTERNATIVE_CFG,
which test for the existence of the callback parameter in inline
assembly using the following expression:

  " .if " __stringify(cb) " == 0\n"

This works with GNU as, but isn't supported by LLVM. This change
splits __ALTERNATIVE_CFG and ALTINSTR_ENTRY into separate macros
to fix the LLVM build.

Bug: 145210207
Change-Id: I62dd786277bcaf3c730a7489c4b5a2b437f722ce
(am from https://lore.kernel.org/patchwork/patch/1136803/)
Link: ClangBuiltLinux/linux#472
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Dakkshesh <dakkshesh5@gmail.com>

arch/arm64/include/asm/alternative.h

@@ -36,7 +36,7 @@ void apply_alternatives(void *start, size_t length);
 	" .byte 662b-661b\n"				/* source len      */ \
 	" .byte 664f-663f\n"				/* replacement len */
 
-#define ALTINSTR_ENTRY_CB(feature, cb)					      \
+#define ALTINSTR_ENTRY_CB(feature,cb)					      \
 	" .word 661b - .\n"				/* label           */ \
 	" .word " __stringify(cb) "- .\n"		/* callback */	      \
 	" .hword " __stringify(feature) "\n"		/* feature bit     */ \
@@ -82,7 +82,7 @@ void apply_alternatives(void *start, size_t length);
 	oldinstr "\n"							\
 	"662:\n"							\
 	".pushsection .altinstructions,\"a\"\n"				\
-	ALTINSTR_ENTRY_CB(feature, cb)					\
+	ALTINSTR_ENTRY_CB(feature,cb)					\
 	".popsection\n"							\
 	"663:\n\t"							\
 	"664:\n\t"							\