target/riscv/kvm.c: read/write (cbom|cboz)_blocksize in KVM

target/riscv/kvm.c: read/write (cbom|cboz)_blocksize in KVM

If we don't set a proper cbom_blocksize|cboz_blocksize in the FDT the
Linux Kernel will fail to detect the availability of the CBOM/CBOZ
extensions, regardless of the contents of the 'riscv,isa' DT prop.

The FDT is being written using the cpu->cfg.cbom|z_blocksize attributes,
so let's expose them as user properties like it is already done with
TCG.

This will also require us to determine proper blocksize values during
init() time since the FDT is already created during realize(). We'll
take a ride in kvm_riscv_init_multiext_cfg() to do it. Note that we
don't need to fetch both cbom and cboz blocksizes every time: check for
their parent extensions (icbom and icboz) and only read the blocksizes
if needed.

In contrast with cbom|z_blocksize properties from TCG, the user is not
able to set any value that is different from the 'host' value when
running KVM. KVM can be particularly harsh dealing with it: a ENOTSUPP
can be thrown for the mere attempt of executing kvm_set_one_reg() for
these 2 regs.

Hopefully we don't need to call kvm_set_one_reg() for these regs.
We'll check if the user input matches the host value in
kvm_cpu_set_cbomz_blksize(), the set() accessor for both blocksize
properties. We'll fail fast since it's already known to not be
supported.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230706101738.460804-21-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>