riscv: clean up the macro format in each header file

There are many different formats in each header now, such as
_ASM_XXX_H, __ASM_XXX_H, _ASM_RISCV_XXX_H, RISCV_XXX_H, etc., This patch
tries to unify the format by using _ASM_RISCV_XXX_H, because the most
header use it now. This patch also adds the conditional to the headers
if they lost it.

Signed-off-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>

arch/riscv/include/asm/pci.h

@@ -3,8 +3,8 @@
  * Copyright (C) 2016 SiFive
  */
 
-#ifndef __ASM_RISCV_PCI_H
-#define __ASM_RISCV_PCI_H
+#ifndef _ASM_RISCV_PCI_H
+#define _ASM_RISCV_PCI_H
 
 #include <linux/types.h>
 #include <linux/slab.h>
@@ -34,4 +34,4 @@ static inline int pci_proc_domain(struct pci_bus *bus)
 }
 #endif  /* CONFIG_PCI */
 
-#endif  /* __ASM_PCI_H */
+#endif  /* _ASM_RISCV_PCI_H */