s390/cpacf: Make use of invalid opcode produce a link error

Instead of calling BUG() at runtime introduce and use a prototype for a
non-existing function to produce a link error during compile when a not
supported opcode is used with the __cpacf_query() or __cpacf_check_opcode()
inline functions.
Suggested-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/cpacf.h

@@ -166,6 +166,13 @@
 
 typedef struct { unsigned char bytes[16]; } cpacf_mask_t;
 
+/*
+ * Prototype for a not existing function to produce a link
+ * error if __cpacf_query() or __cpacf_check_opcode() is used
+ * with an invalid compile time const opcode.
+ */
+void __cpacf_bad_opcode(void);
+
 static __always_inline void __cpacf_query_rre(u32 opc, u8 r1, u8 r2,
 					      cpacf_mask_t *mask)
 {
@@ -237,7 +244,7 @@ static __always_inline void __cpacf_query(unsigned int opcode,
 		__cpacf_query_rre(CPACF_PRNO, 2, 4, mask);
 		break;
 	default:
-		BUG();
+		__cpacf_bad_opcode();
 	}
 }
 
@@ -262,7 +269,8 @@ static __always_inline int __cpacf_check_opcode(unsigned int opcode)
 	case CPACF_KMA:
 		return test_facility(146);	/* check for MSA8 */
 	default:
-		BUG();
+		__cpacf_bad_opcode();
+		return 0;
 	}
 }