x86: x86_msr_op(): Simplify assertions

Simplify them by moving them into more natural places, i.e., default
cases of 'switch' statements.

No functional change (intended).

Reviewed by:    kib
MFC after:      2 weeks
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D54996

sys/x86/x86/cpu_machdep.c

@@ -145,6 +145,8 @@ x86_msr_op_one(void *argp)
 		v = rdmsr(a->msr);
 		*a->res = v;
 		break;
+	default:
+		__assert_unreachable();
 	}
 }
 
@@ -162,13 +164,7 @@ x86_msr_op(u_int msr, u_int op, uint64_t arg1, uint64_t *res)
 	int bound_cpu, cpu, i, is_bound;
 
 	exmode = op & MSR_OP_EXMODE_MASK;
-	MPASS(exmode == MSR_OP_LOCAL || exmode == MSR_OP_SCHED_ALL ||
-	    exmode == MSR_OP_SCHED_ONE || exmode == MSR_OP_RENDEZVOUS_ALL ||
-	    exmode == MSR_OP_RENDEZVOUS_ONE);
-
 	a.op = op & MSR_OP_OP_MASK;
-	MPASS(a.op == MSR_OP_ANDNOT || a.op == MSR_OP_OR ||
-	    a.op == MSR_OP_WRITE || a.op == MSR_OP_READ);
 	a.msr = msr;
 	a.arg1 = arg1;
 	a.res = res;
@@ -219,6 +215,8 @@ x86_msr_op(u_int msr, u_int op, uint64_t arg1, uint64_t *res)
 		smp_rendezvous_cpus(set, smp_no_rendezvous_barrier,
 		    x86_msr_op_one, smp_no_rendezvous_barrier, &a);
 		break;
+	default:
+		__assert_unreachable();
 	}
 }