x86/build: Remove no-op macro VMLINUX_SYMBOL()

VMLINUX_SYMBOL() is no-op unless CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX
is defined.  It has ever been selected only by BLACKFIN and METAG.
VMLINUX_SYMBOL() is unneeded for x86-specific code.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch <linux-arch@vger.kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/1525852174-29022-1-git-send-email-yamada.masahiro@socionext.com

arch/x86/kernel/vmlinux.lds.S

@@ -117,11 +117,11 @@ SECTIONS
 
 #ifdef CONFIG_X86_64
 		. = ALIGN(PAGE_SIZE);
-		VMLINUX_SYMBOL(__entry_trampoline_start) = .;
+		__entry_trampoline_start = .;
 		_entry_trampoline = .;
 		*(.entry_trampoline)
 		. = ALIGN(PAGE_SIZE);
-		VMLINUX_SYMBOL(__entry_trampoline_end) = .;
+		__entry_trampoline_end = .;
 		ASSERT(. - _entry_trampoline == PAGE_SIZE, "entry trampoline is too big");
 #endif