[ucode] Add support for updating x86 microcode

Intel and AMD distribute microcode updates, which are typically
applied by the BIOS and/or the booted operating system.

BIOS updates can be difficult to obtain and cumbersome to apply, and
are often neglected.  Operating system updates may be subject to
strict change control processes, particularly for production
workloads.  There is therefore value in being able to update the
microcode at boot time using a freshly downloaded microcode update
file, particularly in scenarios where the physical hardware and the
installed operating system are controlled by different parties (such
as in a public cloud infrastructure).

Add support for parsing Intel and AMD microcode update images, and for
applying the updates to all CPUs in the system.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/config.c

@@ -188,6 +188,9 @@ REQUIRE_OBJECT ( zlib );
 #ifdef IMAGE_GZIP
 REQUIRE_OBJECT ( gzip );
 #endif
+#ifdef IMAGE_UCODE
+REQUIRE_OBJECT ( ucode );
+#endif
 
 /*
  * Drag in all requested commands

src/config/general.h

@@ -127,6 +127,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define	IMAGE_PEM		/* PEM image support */
 //#define	IMAGE_ZLIB		/* ZLIB image support */
 //#define	IMAGE_GZIP		/* GZIP image support */
+//#define	IMAGE_UCODE		/* Microcode update image support */
 
 /*
  * Command-line commands to include