soc/intel/skylake: add Kabylake Celeron base SKU

soc/intel/skylake: add Kabylake Celeron base SKU

This patch adds the support for Kabylake Celeron base SKU
with PCH ID 0x9d50.

BRANCH=none
BUG=b:65709679

TEST=Ensure coreboot could recognize the Kabylake Celeron base
     SKU and boot into OS.

Change-Id: I9c6f7bf643e0dbeb132fb677fcff461244101a55
Signed-off-by: Tsai, Gaggery <gaggery.tsai@intel.com>
Reviewed-on: https://review.coreboot.org/21617
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: David Wu <david_wu@quantatw.com>
Reviewed-by: T.H. Lin <T.H_Lin@quantatw.com>