hv: fix 'User name starts with underscore'

There are chances that names with leading underscore declared by
developers are conflict with the ones reserved for the compiler.

What this patch does:
- rename these functions/variables/macros starting with
  underscore to avoid such unintentational mistakes.
- remove gpr.h without any contents

Tracked-On: #861
Signed-off-by: Shiqing Gao <shiqing.gao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/include/lib/mem_mgt.h

@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-#ifndef __MEM_MGT_H__
-#define __MEM_MGT_H__
+#ifndef MEM_MGT_H
+#define MEM_MGT_H
 
 /* Macros */
 #define BITMAP_WORD_SIZE         32U
@@ -28,4 +28,4 @@ void *alloc_page(void);
 void *alloc_pages(unsigned int page_num);
 void free(void *ptr);
 
-#endif /* MEM_MGT_H_ */
+#endif /* MEM_MGT_H */