PCI/ASPM: Rename L1.2-specific functions from 'l1ss' to 'l12'

The functions aspm_calc_l1ss_info() and calc_l1ss_pwron() perform
calculations and register programming specific to L1.2 state.  Rename them
to aspm_calc_l12_info() and calc_l12_pwron() respectively.

Link: https://lore.kernel.org/r/20230504111301.229358-5-ajayagarwal@google.com


Signed-off-by: Ajay Agarwal <ajayagarwal@google.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>