mb/google/brya: Add new baseboard nissa with variants nivviks and nereid

Add a new baseboard for nissa, an Intel ADL-N based reference design.
Also, add variants for the two reference boards, nivviks and nereid.
This commit is a stub which only adds the minimum code needed for a
successful build.

BUG=b:197479026
TEST=abuild -a -x -c max -p none -t google/brya -b nivviks
     abuild -a -x -c max -p none -t google/brya -b nereid

Change-Id: I2a3975fb7a45577fec8ea7c6c9f6ea042ab8cba5
Signed-off-by: Reka Norman <rekanorman@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60271
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kangheui Won <khwon@chromium.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>
diff --git a/src/mainboard/google/brya/variants/nivviks/overridetree.cb b/src/mainboard/google/brya/variants/nivviks/overridetree.cb
new file mode 100644
index 0000000..ee86142
--- /dev/null
+++ b/src/mainboard/google/brya/variants/nivviks/overridetree.cb
@@ -0,0 +1,4 @@
+chip soc/intel/alderlake
+        device domain 0 on
+        end
+end