mainboard/intel: Add MinnowBoard 3

This commit adds the initial scaffolding for the MinnowBoard 3
with Apollo Lake silicon.

This mainboard is based on Intel's Leafhill CRB with Apollo Lake
silicon. In a first step, it concerns only a copy of intel/leafhill
directory with name changes. Special adaptations for MinnowBoard 3
mainboard will follow in separate commits.

Change-Id: I7563fe37c89511c7035c5bffc9b034b379cfcaf4
Signed-off-by: Brenton Dong <brenton.m.dong@intel.com>
Reviewed-on: https://review.coreboot.org/18298
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
12 files changed