cmake: Add HX1K-only builds support

Signed-off-by: David Shah <davey1576@gmail.com>

README.md

@@ -21,6 +21,7 @@ Building
 
  - Use CMake to generate the Makefiles (only needs to be done when `CMakeLists.txt` changes)
     - For a debug build, run `cmake -DCMAKE_BUILD_TYPE=Debug .`
+    - For a debug build with HX1K support only, run ` cmake -DCMAKE_BUILD_TYPE=Debug -DICE40_HX1K_ONLY=1 .`
     - For a release build, run `cmake .`
  - Use Make to run the build itself
     - For all targets, just run `make`

ice40/family.cmake

@@ -1,4 +1,12 @@
-set(devices 384 1k 5k 8k)
+if(ICE40_HX1K_ONLY)
+    set(devices 1k)
+    foreach (target ${family_targets})
+        target_compile_definitions(${target} PRIVATE ICE40_HX1K_ONLY=1)
+    endforeach (target)
+else()
+    set(devices 384 1k 5k 8k)
+endif()
+
 set(DB_PY ${CMAKE_CURRENT_SOURCE_DIR}/ice40/chipdb.py)
 file(MAKE_DIRECTORY ice40/chipdbs/)
 add_library(ice40_chipdb OBJECT ice40/chipdbs/)