x86/msr: Rename the WRMSRNS opcode macro to ASM_WRMSRNS (for KVM)

Rename the WRMSRNS instruction opcode macro so that it doesn't collide
with X86_FEATURE_WRMSRNS when using token pasting to generate references
to X86_FEATURE_WRMSRNS.  KVM heavily uses token pasting to generate KVM's
set of support feature bits, and adding WRMSRNS support in KVM will run
will run afoul of the opcode macro.

  arch/x86/kvm/cpuid.c:719:37: error: pasting "X86_FEATURE_" and "" "" does not
                                      give a valid preprocessing token
  719 |         u32 __leaf = __feature_leaf(X86_FEATURE_##name);                \
      |                                     ^~~~~~~~~~~~

KVM has worked around one such collision in the past by #undef'ing the
problematic macro in order to avoid blocking a KVM rework, but such games
are generally undesirable, e.g. requires bleeding macro details into KVM,
risks weird behavior if what KVM is #undef'ing changes, etc.

Reviewed-by: Xin Li (Intel) <xin@zytor.com>
Link: https://lore.kernel.org/r/20250227010111.3222742-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/include/asm/msr.h

@@ -300,7 +300,7 @@ do {							\
 #endif	/* !CONFIG_PARAVIRT_XXL */
 
 /* Instruction opcode for WRMSRNS supported in binutils >= 2.40 */
-#define WRMSRNS _ASM_BYTES(0x0f,0x01,0xc6)
+#define ASM_WRMSRNS _ASM_BYTES(0x0f,0x01,0xc6)
 
 /* Non-serializing WRMSR, when available.  Falls back to a serializing WRMSR. */
 static __always_inline void wrmsrns(u32 msr, u64 val)
@@ -309,7 +309,7 @@ static __always_inline void wrmsrns(u32 msr, u64 val)
 	 * WRMSR is 2 bytes.  WRMSRNS is 3 bytes.  Pad WRMSR with a redundant
 	 * DS prefix to avoid a trailing NOP.
 	 */
-	asm volatile("1: " ALTERNATIVE("ds wrmsr", WRMSRNS, X86_FEATURE_WRMSRNS)
+	asm volatile("1: " ALTERNATIVE("ds wrmsr", ASM_WRMSRNS, X86_FEATURE_WRMSRNS)
 		     "2: " _ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_WRMSR)
 		     : : "c" (msr), "a" ((u32)val), "d" ((u32)(val >> 32)));
 }