nb/intel/ironlake: Move register headers into a subfolder

Move all files with register definitions into a `registers` subfolder.
Subsequent commits will move the remaining registers into this folder.

Tested with BUILD_TIMELESS=1, Packard Bell MS2290 remains identical.

Change-Id: I872269ca3c7fbbcffe83327a20bcf8d98b356beb
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45381
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/northbridge/intel/ironlake/ironlake.h

@@ -43,7 +43,7 @@
 
 /* Device 0:0.0 PCI configuration space (Host Bridge) */
 
-#include "hostbridge_regs.h"
+#include "registers/host_bridge.h"
 
 /*
  * Generic Non-Core Registers