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/arch/x86/cpu.c

@@ -388,8 +388,8 @@ void bsp_boot_init(void)
 	start_tsc = rdtsc();
 
 	/* Clear BSS */
-	(void)memset(&_ld_bss_start, 0U,
-			(size_t)(&_ld_bss_end - &_ld_bss_start));
+	(void)memset(&ld_bss_start, 0U,
+			(size_t)(&ld_bss_end - &ld_bss_start));
 
 	bitmap_set_nolock(BOOT_CPU_ID, &pcpu_active_bitmap);