feat: implement utime libc function, SYS_UTIME syscall, filesystem support (ext2 only)

kernel/src/Fs/Boot.cpp

@@ -101,6 +101,7 @@ namespace Fs {
             .GetLabel  = RdGetLabel,
             .ReadDirAt = RdReadDirAt,
             .Stat      = RdStat,
+            .SetTimes  = nullptr,
             // Statically allocated: nothing to release.
             .Unmount   = nullptr,
         };