System calls implemented:
- shutdown: System shutdown with sbi_shutdown()
- times: Process time information with tms structure
- uname: System information with utsname structure
- getcwd: Modified to return buffer address for test compatibility
- write/getpid: Maintained existing functionality

Platform evaluation features:
- Makefile with 'all' target generating kernel-qemu and sbi-qemu
- Automatic test case discovery from SD card
- Sequential test execution with serial output
- Automatic shutdown after test completion
- Support for test_getcwd, test_write, test_getpid, test_times, test_uname

Files ready for evaluation platform.