linuxkpi: Define pat_enabled()

This new <asm/memtype.h> header is included from <linux/pci.h> because
that's how it is included in Linux too. DRM drivers depend on this.

Reviewed by:	manu
Approved by:	manu
Differential Revision:	https://reviews.freebsd.org/D39052

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

@@ -0,0 +1,18 @@
+/* Public domain. */
+
+#ifndef _LINUXKPI_ASM_MEMTYPE_H_
+#define _LINUXKPI_ASM_MEMTYPE_H_
+
+#if defined(__amd64__) || defined(__i386__)
+
+#include <asm/cpufeature.h>
+
+static inline bool
+pat_enabled(void)
+{
+	return (boot_cpu_has(X86_FEATURE_PAT));
+}
+
+#endif
+
+#endif /* _LINUXKPI_ASM_MEMTYPE_H_ */

sys/compat/linuxkpi/common/include/linux/pci.h

@@ -57,6 +57,7 @@
 #include <linux/compiler.h>
 #include <linux/errno.h>
 #include <asm/atomic.h>
+#include <asm/memtype.h>
 #include <linux/device.h>
 #include <linux/pci_ids.h>
 #include <linux/pm.h>