[AArch64] Add new v9.4-A PM pstate system register

This adds support for the new PM pstate system register introduced by
the v9.4-A Exception-based Event Profiling extension (FEAT_EBEP).

The new PM pstate register takes a 1-bit immediate and requires
different values to be specified for the higher bits of the Crm field.
To enable that, this patch creates an explicit separation between the
pstate system registers that take 4-bit and 1-bit immediate operands,
allowing each entry to specify the value for the 3 high bits of Crm.

This also updates other pstate registers to correctly accept 4-bit
immediates, matching their decoding specification from the Arm ARM.
These include: `PAN`,  `UAO`, `DIT` and `SSBS`.

More information about this extension and the new register can be found
at:
* https://developer.arm.com/documentation/ddi0601/2022-09/AArch64-Registers/PM--PMU-Exception-Mask

Contributors:
* Lucas Prates
* Sam Elliott

Reviewed By: lenary

Differential Revision: https://reviews.llvm.org/D139925