libpayload/x86/delay: Add an x86 arch_ndelay

This method has a pause instruction to help the CPU relax a little bit.
Measuring grunt it saves about 80mW.

BUG=b:109749762
TEST=Made sure that grunt boots.

Change-Id: I045a941ed42fcc4f2dbdd65b5cbb42d84813f50c
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://review.coreboot.org/28244
Reviewed-by: Martin Roth <martinroth@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/libpayload/arch/x86/Makefile.inc

@@ -35,6 +35,7 @@ libc-y += timer.c coreboot.c util.S
 libc-y += exec.S virtual.c
 libc-y += selfboot.c
 libc-y += exception_asm.S exception.c
+libc-y += delay.c
 
 # Will fall back to default_memXXX() in libc/memory.c if GPL not allowed.
 libc-$(CONFIG_LP_GPL) += string.c