One of the existing reserved fields in the microcode header has been
allocated to indicate the size of metadata structures.

The location of metadata section within microcode header is as shown
below:

    Microcode Blob Format
   +----------------------+  Base
   |Header Version        |
   +----------------------+
   |Update revision       |
   +----------------------+
   |Date DDMMYYYY         |
   +----------------------+
   |Sig                   |
   +----------------------+
   |Checksum              |
   +----------------------+
   |Loader Version        |
   +----------------------+
   |Processor Flags       |
   +----------------------+
   |Data Size             |
   +----------------------+
   |Total Size            |
   +----------------------+
   |Meta Size             |
   +----------------------+
   |Reserved              |
   +----------------------+
   |Reserved              |
   +----------------------+  Base+48
   |                      |
   |    Microcode         |
   |     Data             |
   |                      |
   +----------------------+  Base+48+data_size-
   |                      |     meta_size
   |   Meta Data          |
   |   structure(s)       |
   |                      |
   +----------------------+  Base+48+data_size
   |                      |
   |   Extended Signature |
   |        Table         |
   |                      |
   +----------------------+  Base+total_size

Add an accessor function which will return a pointer to the start of a
specific meta_type being queried.

  [ bp: Massage commit message. ]
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Jithu Joseph <jithu.joseph@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20221117035935.4136738-11-jithu.joseph@intel.com