Documentation/soc/intel/fsp: Move mp_service_ppi document in corrct directory

This patch moves mp service ppi document from icelake/MultiProcesorInit.md
to ppi/mp_service_ppi.c.

Change-Id: I1bbaeb2644f219b5a1fda0c7c4b594184d53958c
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/31840
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/soc/intel/fsp/ppi/ppi.md

@@ -7,3 +7,8 @@ where FSP should be able to locate PPI, published by boot firmware and
 able to execute the same in FSP's context.
 
 * [What is PPI](https://www.intel.com/content/dam/www/public/us/en/documents/reference-guides/efi-pei-cis-v09.pdf)
+
+## List of PPI service
+
+### Publish MP Service PPI from boot firmware (coreboot) to initialize CPU
+- [MP Service PPI](mp_service_ppi.md)

Documentation/soc/intel/icelake/index.md

@@ -5,7 +5,3 @@ This section contains documentation about coreboot on specific Intel "Ice Lake"
 ## Ice Lake coreboot development
 
 - [Ice Lake coreboot development](iceLake_coreboot_development.md)
-
-## Multiprocessor Init
-
-- [Multiprocessor Init](MultiProcessorInit.md)