cpu/intel/microcode: Add caching layer in intel_microcode_find

Cache the found microcode for faster subsequent accesses.

Change-Id: Ic40d57964600f8f20ddb26c7d1691b043fd89f29
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49896
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cpu/intel/microcode.h

@@ -6,8 +6,10 @@
 
 void intel_update_microcode_from_cbfs(void);
 /* Find a microcode that matches the revision and platform family returning
- * NULL if none found. */
+ * NULL if none found. The found microcode is cached for faster access on
+ * subsequent calls of this function. */
 const void *intel_microcode_find(void);
+
 /* It is up to the caller to determine if parallel loading is possible as
  * well as ensuring the microcode matches the family and revision (i.e. with
  * intel_microcode_find()). */