amd-xgbe: add support for P100a platform

amd-xgbe: add support for P100a platform

Add hardware support for the AMD P100a platform featuring the ethernet
controller PCI device ID 0x1122.

Platform-specific changes include:

1. PCI device ID and register configuration:
   - Add XGBE_P100a_PCI_DEVICE_ID (0x1122) for recognition
   - Configure platform-specific XPCS window registers
   - Disable CDR workaround and RRC for this platform

2. XPCS window offset calculation fix:
   The P100a platform uses a different memory mapping scheme for XPCS
   register access. The offset calculation differs between platforms:

   - Older platforms (YC): offset = base + (addr & mask)
     The address is masked first, then added to the window base.

   - P100a: offset = (base + addr) & mask
     The full address is added to base first, then masked.

   This is critical because using the wrong calculation causes register
   reads/writes to access incorrect addresses, leading to incorrect
   behaviour.

3. 2.5G speed mode handling:
   P100a uses XGMII mode (ss=0x06) for 2.5G instead of GMII mode
   (ss=0x02) used by older platforms. The MAC version check determines
   which mode to use.

4. Port speed bits extended:
   Extend XP_PROP_0_PORT_SPEEDS from 5 bits to 6 bits to support the
   additional 5G speed capability.

5. Rx adaptation disabled:
   Rx adaptation is disabled for P100a (MAC version 0x33) as this
   feature requires further development for this platform.

6. Rate change command for 2.5G:
   Use XGBE_MB_SUBCMD_2_5G_KX subcommand for 2.5G mode on P100a
   instead of XGBE_MB_SUBCMD_NONE used on older platforms.

Signed-off-by: Raju Rangoju <Raju.Rangoju@amd.com>
Link: https://patch.msgid.link/20260302044634.1388661-2-Raju.Rangoju@amd.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>