soc/intel: common,skl,cnl,icl: drop reserved mmio memory size calculation

Remove the calculation of the Reserved Intel MMIO Memory size from
systemagent and memmap, since it is not needed.

The size is used in SA to calculate the space between cbmem_top and TSEG
without DPR and Chipset Reserved Memory. Since this will always be equal
to 0, the reservation will be skipped and TSEG, DPR and Chipset Reserved
Memory will get reserved alltogether.

By reading the code and pratical testing we figured out that:
- TSEG - DPR - reserved - top_of_memory == 0
- TSEG - DPR - reserved == top_of_memory

This means the whole block will never reserve anything because it is
always 0. Hence the code can be removed for simplification.

Tested successfully on X11SSM-F

Change-Id: I0cc730551eb3a79c78a971b40056de8d029f4b82
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36216
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Michael Niewöhner
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/cannonlake/memmap.c

@@ -211,21 +211,6 @@ static uintptr_t calculate_dram_base(size_t *reserved_mem_size)
 	return dram_base;
 }
 
-/*
- * SoC implementation
- *
- * SoC call to summarize all Intel Reserve MMIO size and report to SA
- */
-size_t soc_reserved_mmio_size(void)
-{
-	struct ebda_config cfg;
-
-	retrieve_ebda_object(&cfg);
-
-	/* Get Intel Reserved Memory Range Size */
-	return cfg.reserved_mem_size;
-}
-
 /* Fill up memory layout information */
 void fill_soc_memmap_ebda(struct ebda_config *cfg)
 {