target/riscv/tcg: add 'zic64b' support

zic64b is defined in the RVA22U64 profile [1] as a named feature for
"Cache blocks must be 64 bytes in size, naturally aligned in the address
space". It's a fantasy name for 64 bytes cache blocks. The RVA22U64
profile mandates this feature, meaning that applications using this
profile expects 64 bytes cache blocks.

To make the upcoming RVA22U64 implementation complete, we'll zic64b as
a 'named feature', not a regular extension. This means that:

- it won't be exposed to users;
- it won't be written in riscv,isa.

This will be extended to other named extensions in the future, so we're
creating some common boilerplate for them as well.

zic64b is default to 'true' since we're already using 64 bytes blocks.
If any cache block size (cbo{m,p,z}_blocksize) is changed to something
different than 64, zic64b is set to 'false'.

Our profile implementation will then be able to check the current state
of zic64b and take the appropriate action (e.g. throw a warning).

[1] https://github.com/riscv/riscv-profiles/releases/download/v1.0/profiles.pdf

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: <20231218125334.37184-7-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -1443,6 +1443,12 @@ const RISCVCPUMultiExtConfig riscv_cpu_experimental_exts[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
+const RISCVCPUMultiExtConfig riscv_cpu_named_features[] = {
+    MULTI_EXT_CFG_BOOL("zic64b", zic64b, true),
+
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 /* Deprecated entries marked for future removal */
 const RISCVCPUMultiExtConfig riscv_cpu_deprecated_exts[] = {
     MULTI_EXT_CFG_BOOL("Zifencei", ext_zifencei, true),