target/riscv/tcg: do not use "!generic" CPU checks

target/riscv/tcg: do not use "!generic" CPU checks

Our current logic in get/setters of MISA and multi-letter extensions
works because we have only 2 CPU types, generic and vendor, and by using
"!generic" we're implying that we're talking about vendor CPUs. When adding
a third CPU type this logic will break so let's handle it beforehand.

In set_misa_ext_cfg() and set_multi_ext_cfg(), check for "vendor" cpu instead
of "not generic". The "generic CPU" checks remaining are from
riscv_cpu_add_misa_properties() and cpu_add_multi_ext_prop() before
applying default values for the extensions.

This leaves us with:

- vendor CPUs will not allow extension enablement, all other CPUs will;

- generic CPUs will inherit default values for extensions, all others
  won't.

And now we can add a new, third CPU type, that will allow extensions to
be enabled and will not inherit defaults, without changing the existing
logic.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231218125334.37184-3-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>