egl: Move _eglPointerIsDereferencable() to eglglobals.[ch]

Move _eglPointerIsDereferencable() to eglglobals.[ch] and make it a
non-static function so it can be used out of egldisplay.c

Signed-off-by: Miguel A. Vico <mvicomoya@nvidia.com>
Reviewed-by: James Jones <jajones@nvidia.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

src/egl/main/eglglobals.c

@@ -37,6 +37,12 @@
 #include "eglglobals.h"
 #include "egldisplay.h"
 #include "egldriver.h"
+#include "egllog.h"
+
+#ifdef HAVE_MINCORE
+#include <unistd.h>
+#include <sys/mman.h>
+#endif
 
 
 static mtx_t _eglGlobalMutex = _MTX_INITIALIZER_NP;
@@ -142,3 +148,28 @@ _eglGetClientExtensionString(void)
    mtx_unlock(_eglGlobal.Mutex);
    return ret;
 }
+
+EGLBoolean
+_eglPointerIsDereferencable(void *p)
+{
+#ifdef HAVE_MINCORE
+   uintptr_t addr = (uintptr_t) p;
+   unsigned char valid = 0;
+   const long page_size = getpagesize();
+
+   if (p == NULL)
+      return EGL_FALSE;
+
+   /* align addr to page_size */
+   addr &= ~(page_size - 1);
+
+   if (mincore((void *) addr, page_size, &valid) < 0) {
+      _eglLog(_EGL_DEBUG, "mincore failed: %m");
+      return EGL_FALSE;
+   }
+
+   return (valid & 0x01) == 0x01;
+#else
+   return p != NULL;
+#endif
+}