Merge patch series "make write_misa a no-op and FEATURE_* cleanups"

Daniel Henrique Barboza <dbarboza@ventanamicro.com> says:

The RISCV_FEATURES_* enum and the CPUArchState::features attribute were
introduced 4+ years ago, as a way to retrieve the enabled hart features
that aren't represented via MISA CSR bits. Time passed on, and
RISCVCPUConfig was introduced. With it, we now have a centralized way of
reading all hart features that are enabled/disabled by the user and the
board. All recent features are reading their correspondent cpu->cfg.X
flag.

All but the 5 features in the RISCV_FEATURE_* enum. These features are
still operating in the same way: set it during riscv_cpu_realize() using
their cpu->cfg value, read it using riscv_feature() when needed. There
is nothing special about them in comparison with all the other features
and extensions to justify this special handling.

This series then is doing two things: first we're actually allowing
users to write the MISA CSR if they so choose. Then we're deprecate each
RISC_FEATURE_* usage until, in patch 11, we remove everything related to
it. All 5 existing RISCV_FEATURE_* features will be handled as everyone
else.

* b4-shazam-merge:
  target/riscv/cpu: remove CPUArchState::features and friends
  target/riscv: remove RISCV_FEATURE_MMU
  hw/riscv/virt.c: do not use RISCV_FEATURE_MMU in create_fdt_socket_cpus()
  target/riscv: remove RISCV_FEATURE_PMP
  target/riscv: remove RISCV_FEATURE_EPMP
  target/riscv/cpu.c: error out if EPMP is enabled without PMP
  target/riscv: remove RISCV_FEATURE_DEBUG
  target/riscv: allow MISA writes as experimental
  target/riscv: do not mask unsupported QEMU extensions in write_misa()
  target/riscv: introduce riscv_cpu_cfg()

Message-ID: <20230222185205.355361-1-dbarboza@ventanamicro.com>
[Palmer: use the text from the v1]
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>