[Libreboot] T400 (gm45?) RTC fix

[Bella Riosa]

Issue: Kernels newer than 4.2 couldn't read the hw-clock and set the date to 
1.1.1970
On Kernels up to 4.2 this kernel message appears (but the hw-clock works):

WARNING: Persistent clock returned invalid value!
Check your CMOS/BIOS settings.


Fix:
1. Apply https://review.coreboot.org/#/c/11853/ 
2. flash and reboot
3. use nvramtool and a hex-editor to patch the cmos century-byte (byte# 0x32)
it must be 0x20 (yes hex, it's BCD)
4. reboot again. it should work now