x86, MCE, FIX MSR_IA32_MCI_CTL2_CMCI threshold setup (resend)

Changelog:

v3:

- Separate patch into 2 patches, one for renaming, the other for threshold setup fixing.

v2:

- Rename CMCI_EN to MCI_CTL2_CMCI_EN and CMCI_THRESHOLD_MASK to MCI_CTL2_CMCI_THRESHOLD_MASK to make naming consistent.