cdx: Split mcdi.h and reorganize headers

Move bitfield.h from the CDX controller directory to include/linux/cdx to make
them accessible to other drivers.

As part of this refactoring, split mcdi.h into two headers:

- mcdi.h: retains interface-level declarations
- mcdid.h: contains internal definitions and macros

This is in preparation for VersalNET EDAC driver that relies on it.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
Link: https://lore.kernel.org/20250908115649.22903-1-shubhrajyoti.datta@amd.com

drivers/cdx/controller/mcdi.c

@@ -23,9 +23,10 @@
 #include <linux/log2.h>
 #include <linux/net_tstamp.h>
 #include <linux/wait.h>
+#include <linux/cdx/bitfield.h>
 
-#include "bitfield.h"
-#include "mcdi.h"
+#include <linux/cdx/mcdi.h>
+#include "mcdid.h"
 
 static void cdx_mcdi_cancel_cmd(struct cdx_mcdi *cdx, struct cdx_mcdi_cmd *cmd);
 static void cdx_mcdi_wait_for_cleanup(struct cdx_mcdi *cdx);