soc/intel/skylake: Use EBDA structure to store soc reserve memory size

soc/intel/skylake: Use EBDA structure to store soc reserve memory size

Avoid calling calculate_dram_base() function to get chipset reserved
memory size during pci resource allocation. Rather use EBDA to store
chipset reserved memory size while calling cbmem_top_int().

This patch avoids one extra calculate_dram_base() call.

BRANCH=none
BUG=b:63974384
TEST=Ensures DRAM based resource allocation has taken care of Intel
SoC reserved ranges.

Change-Id: I52f359db5a712179d7f2accb4d323d759f3b052b
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/22098
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>