soc/intel/cannonlake: Add field to identify single channel memory

soc/intel/cannonlake: Add field to identify single channel memory

Variants of Hatch need to accommodate single channel DDR.  Also,
removing const modifier as we'll need to set these fields
incrementally now.  For the single channel configuration, we set
MemorySpdPtr10 to 0.  For the dual channel configuration, we set
MemorySpdPtr10 to MemorySpdPtr00.

BUG=b:123062346, b:122959294
BRANCH=None
TEST=Boot into current boards and ensure that we have 2 channels as expected

Change-Id: Ice22b103664187834e255d1359bfd9b51993b5b6
Signed-off-by: Shelley Chen <shchen@google.com>
Reviewed-on: https://review.coreboot.org/c/31262
Reviewed-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>