[lldb][AArch64][Linux] Add register field information for SME's SVCR register (#71809)

This register is a pseudo register but mirrors the architectural
register's contents. See:
https://developer.arm.com/documentation/ddi0616/latest/

For the full details. Example output:
```
(lldb) register read svcr
    svcr = 0x0000000000000002
         = (ZA = 1, SM = 0)
```