surtr: use usingnamespace to export ach code

Signed-off-by: smallkirby <[email protected]>

surtr/arch.zig

@@ -1,7 +1,7 @@
 //! Thin wrapper to access arch-specific modules.
 
 const builtin = @import("builtin");
-pub const impl = switch (builtin.target.cpu.arch) {
+pub usingnamespace switch (builtin.target.cpu.arch) {
     .x86_64 => @import("arch/x86/arch.zig"),
     else => @compileError("Unsupported architecture."),
 };

surtr/boot.zig

@@ -14,7 +14,7 @@ const log = std.log.scoped(.surtr);
 
 const blog = @import("log.zig");
 const defs = @import("defs.zig");
-const arch = @import("arch.zig").impl;
+const arch = @import("arch.zig");
 
 const page_size = arch.page.page_size_4k;
 const page_mask = arch.page.page_mask_4k;