src/soc/intel/cannonlake: Bump MAX_CPU from 8->12

src/soc/intel/cannonlake: Bump MAX_CPU from 8->12

This impacts boards:
 hatch (&variants) and drallion.

Some variants like Puff can have up to 12 cores. coreboot should take
the min() where MAX_CPU is the upper bound.

Further to that, boards themseleves shouldn't be setting the MAX_CPUS,
the chipset should be and so do that.

BRANCH=none
BUG=b:146255011
TEST=./util/abuild/abuild -p none -t google/hatch -x -a

Change-Id: I284d027886f662ebb8414ea92540916ed19bc797
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37725
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: EricR Lai <ericr_lai@compal.corp-partner.google.com>
Reviewed-by: Shelley Chen <shchen@google.com>
Reviewed-by: Mathew King <mathewk@chromium.org>