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/crypto/sha1.c

@@ -30,7 +30,7 @@ typedef unsigned int u_int;
 
 /* Moved from libpayload.h */
 
-#ifdef CONFIG_TARGET_I386
+#ifdef CONFIG_ARCH_X86
 #define BYTE_ORDER      LITTLE_ENDIAN
 #else
 #define BYTE_ORDER      BIG_ENDIAN