Specify device for stm32 (#889)

Instead of having to ingest and generate all the register information
for all stm32 chips, give regz the ability to only generate for one.
This has the added benefit that when you look at the generated code, you
only see the peripheral types that are used by your device.

Author: mattnite

build-internals/build.zig

@@ -142,8 +142,11 @@ pub const Chip = struct {
         /// Use the provided file directly as the chip file.
         zig: LazyPath,
 
-        /// Path to embassy stm32-data directory
-        embassy: LazyPath,
+        /// Path to embassy stm32-data directory with optional device filter
+        embassy: struct {
+            path: LazyPath,
+            device: ?[]const u8 = null,
+        },
 
         /// Single device from TI targetdb
         targetdb: struct {

build.zig

@@ -416,7 +416,7 @@ pub fn MicroBuild(port_select: PortSelect) type {
                     regz_run.addFileArg(file);
                     break :blk chips_dir.path(b, b.fmt("{s}.zig", .{target.chip.name}));
                 },
-                .embassy => |path| blk: {
+                .embassy => |embassy| blk: {
                     const regz_run = b.addRunArtifact(regz_exe);
 
                     regz_run.addArg("--format");
@@ -430,7 +430,12 @@ pub fn MicroBuild(port_select: PortSelect) type {
                         regz_run.addFileArg(patch_file);
                     }
 
-                    regz_run.addDirectoryArg(path);
+                    if (embassy.device) |device| {
+                        regz_run.addArg("--device");
+                        regz_run.addArg(device);
+                    }
+
+                    regz_run.addDirectoryArg(embassy.path);
                     break :blk chips_dir.path(b, b.fmt("{s}.zig", .{target.chip.name}));
                 },
                 .targetdb => |targetdb| blk: {