Change TARGET_I386 to ARCH_X86

This renames TARGET_I386 to ARCH_X86 to make it more uniform with
other parts of the codebase, e.g. cbfs_core.h from cbfstool.

Change-Id: I1babcc941245ed1dde0478a21828766759373a42
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/1961
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Dave Frodin <dave.frodin@se-eng.com>

payloads/libpayload/libc/time.c

@@ -34,7 +34,7 @@
 
 #include <libpayload-config.h>
 #include <libpayload.h>
-#ifdef CONFIG_TARGET_I386
+#ifdef CONFIG_ARCH_X86
 #include <arch/rdtsc.h>
 #endif
 
@@ -49,7 +49,7 @@ static struct {
 #define TICKS_PER_SEC (cpu_khz * 1000)
 #define TICKS_PER_USEC (cpu_khz / 1000)
 
-#ifdef CONFIG_TARGET_I386
+#ifdef CONFIG_ARCH_X86
 static void update_clock(void)
 {
 	u64 delta = rdtsc() - clock.ticks;