riscv: Add support for srmcfg CSR from Ssqosid extension

Add support for the srmcfg CSR defined in the Ssqosid ISA extension.
The CSR contains two fields:

  - Resource Control ID (RCID) for resource allocation
  - Monitoring Counter ID (MCID) for tracking resource usage

Requests from a hart to shared resources are tagged with these IDs,
allowing resource usage to be associated with the running task.

Add a srmcfg field to thread_struct with the same format as the CSR.
The context-switch path writes the field to the CSR, and
resctrl_arch_set_closid_rmid() updates it when a task is assigned to a
resctrl control or monitoring group.

A per-cpu cpu_srmcfg_default holds the default srmcfg for each CPU, set
by resctrl_arch_set_cpu_default_closid_rmid() on CPU group assignment.
On context switch, RCID and MCID inherit from the CPU default
independently: a task whose thread RCID field is zero takes the CPU
default's RCID, and likewise for MCID.

A per-cpu cpu_srmcfg variable mirrors the CSR state to avoid
redundant writes. L1D-hot memory access is faster than a CSR read and
avoids traps under virtualization.

Link: https://github.com/riscv/riscv-ssqosid/releases/tag/v1.0
Assisted-by: Claude:claude-opus-4-7
Co-developed-by: Kornel Dulęba <mindal@semihalf.com>
Signed-off-by: Kornel Dulęba <mindal@semihalf.com>
Signed-off-by: Drew Fustini <fustini@kernel.org>
Link: https://patch.msgid.link/20260729-dfustini-atl-sc-cbqri-dt-v6-3-7c22b05d461b@kernel.org
Signed-off-by: Paul Walmsley <pjw@kernel.org>

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