all: use root boot info pointer

src/kern/tunable.zig

@@ -42,8 +42,8 @@ pub fn Tunable(comptime T: type, comptime default: T, comptime name: []const u8)
     };
 }
 
-pub fn init(boot_info: *r.BootInfo) void {
-    const cmdline = boot_info.cmdline orelse return;
+pub fn init() void {
+    const cmdline = r.boot_info.cmdline orelse return;
 
     const elems = set.elems();