LinuxKPI: Add static_cpu_has() implementation

static_cpu_has returns true if CPU supports requested feature.

Obtained from:	OpenBSD
MFC after:	1 week
Reviewed by:	hselasky, manu
Differential Revision:	https://reviews.freebsd.org/D33301

sys/compat/linuxkpi/common/include/asm/cpufeature.h

@@ -0,0 +1,37 @@
+/* Public domain. */
+
+#ifndef _ASM_CPUFEATURE_H
+#define _ASM_CPUFEATURE_H
+
+#if defined(__amd64__) || defined(__i386__)
+
+#include <sys/types.h>
+#include <machine/md_var.h>
+
+#define	X86_FEATURE_CLFLUSH	1
+#define	X86_FEATURE_XMM4_1	2
+#define	X86_FEATURE_PAT		3
+#define	X86_FEATURE_HYPERVISOR	4
+
+static inline bool
+static_cpu_has(uint16_t f)
+{
+	switch (f) {
+	case X86_FEATURE_CLFLUSH:
+		return ((cpu_feature & CPUID_CLFSH) != 0);
+	case X86_FEATURE_XMM4_1:
+		return ((cpu_feature2 & CPUID2_SSE41) != 0);
+	case X86_FEATURE_PAT:
+		return ((cpu_feature & CPUID_PAT) != 0);
+	case X86_FEATURE_HYPERVISOR:
+		return ((cpu_feature2 & CPUID2_HV) != 0);
+	default:
+		return (false);
+	}
+}
+
+#define	boot_cpu_has(x)	static_cpu_has(x)
+
+#endif
+
+#endif