Change in coreboot[master]: drivers/intel/fsp2_0: Add support for MP services2 PPI

[Tim Wawrzynczak (Code Review)]

Attention is currently required from: Furquan Shaikh, Martin Roth, Meera Ravindranath, Aamir Bohra, Tim Wawrzynczak, Andrey Petrov, Patrick Rudolph.
Tim Wawrzynczak has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/49474 )

Change subject: drivers/intel/fsp2_0: Add support for MP services2 PPI
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Patch Set 8:

(3 comments)

File src/drivers/intel/fsp2_0/Kconfig:

https://review.coreboot.org/c/coreboot/+/49474/comment/0e41f421_004d225d 
PS6, Line 267: 
             : if FSP_PEIM_TO_PEIM_INTERFACE
             : source "src/drivers/intel/fsp2_0/ppi/Kconfig"
             : endif
             :
> This gets sourced from src/Makefile. […]

It's redundant, src/Kconfig already has `source "src/drivers/*/*/*/Kconfig`

File src/drivers/intel/fsp2_0/include/fsp/ppi/mp_service_ppi.h:

https://review.coreboot.org/c/coreboot/+/49474/comment/76689570_0a115e84 
PS6, Line 49: /*
            :  * switches the requested AP to be the BSP
            :  */
            : efi_return_status_t mp_switch_bsp(void);
            : 
            : /*
            :  * enable or disable an AP. This service may only be called from the BSP.
            :  */
            : efi_return_status_t mp_enable_disable_ap(void);
            :
> we can keep them as placeholders for now? Is it ok?

We could just have a `efi_return_status_t fsp_ppi_unsupported(void) { return FSP_UNSUPPORTED; }` as an example and use that function pointer instead

File src/drivers/intel/fsp2_0/ppi/mp_service1.c:

https://review.coreboot.org/c/coreboot/+/49474/comment/69cc8a09_81ef060f 
PS6, Line 12: 
nit: extra lines