platform/x86/intel/ifs: Use generic microcode headers and functions

Existing implementation (broken) of IFS used a header format (for IFS
test images) which was very similar to microcode format, but didn’t
accommodate extended signatures. This meant same IFS test image had to
be duplicated for different steppings and the validation code in the
driver was only looking at the primary header parameters. Going forward,
IFS test image headers have been tweaked to become fully compatible with
the microcode format.

Newer IFS test image headers will use header version 2 in order to
distinguish it from microcode images and older IFS test images.

In light of the above, reuse struct microcode_header_intel directly in
the IFS driver and reuse microcode functions for validation and sanity
checking.

  [ bp: Massage commit message. ]

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/20221117225039.30166-1-jithu.joseph@intel.com