feat(cpu): implement format 6 THUMB instructions

src/cpu/thumb/format6.zig

@@ -0,0 +1,16 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+pub fn format6(comptime rd: u3) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u16) void {
+            const offset = (opcode & 0xFF) << 2;
+
+            // FIXME: Should this overflow?
+            cpu.r[rd] = bus.read32((cpu.fakePC() & 0xFFFF_FFFC) + offset);
+        }
+    }.inner;
+}