target/riscv/tcg: remove RVG warning

target/riscv/tcg: remove RVG warning

Vendor CPUs that set RVG are displaying user warnings about other
extensions that RVG must enable, one warning per CPU. E.g.:

$ ./build/qemu-system-riscv64 -smp 8 -M virt -cpu veyron-v1 -nographic
qemu-system-riscv64: warning: Setting G will also set IMAFD_Zicsr_Zifencei
qemu-system-riscv64: warning: Setting G will also set IMAFD_Zicsr_Zifencei
qemu-system-riscv64: warning: Setting G will also set IMAFD_Zicsr_Zifencei
qemu-system-riscv64: warning: Setting G will also set IMAFD_Zicsr_Zifencei
qemu-system-riscv64: warning: Setting G will also set IMAFD_Zicsr_Zifencei
qemu-system-riscv64: warning: Setting G will also set IMAFD_Zicsr_Zifencei
qemu-system-riscv64: warning: Setting G will also set IMAFD_Zicsr_Zifencei
qemu-system-riscv64: warning: Setting G will also set IMAFD_Zicsr_Zifencei

This happens because we decided a while ago that, for simplicity, vendor
CPUs could set RVG instead of setting each G extension individually in
their cpu_init(). Our warning isn't taking that into account, and we're
bugging users with a warning that we're causing ourselves.

In a closer look we conclude that this warning is not warranted in any
other circumstance since we're just following the ISA [1], which states
in chapter 24:

"One goal of the RISC-V project is that it be used as a stable software
development target. For this purpose, we define a combination of a base
ISA (RV32I or RV64I) plus selected standard extensions (IMAFD, Zicsr,
Zifencei) as a 'general-purpose' ISA, and we use the abbreviation G for
the IMAFDZicsr Zifencei combination of instruction-set extensions."

With this in mind, enabling IMAFD_Zicsr_Zifencei if the user explicitly
enables 'G' is an expected behavior and the warning is unneeded. Any
user caught by surprise should refer to the ISA.

Remove the warning when handling RVG.

[1] https://github.com/riscv/riscv-isa-manual/releases/download/Ratified-IMAFDQC/riscv-spec-20191213.pdf

Reported-by: Paul A. Clarke <pclarke@ventanamicro.com>
Suggested-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Message-ID: <20231003122539.775932-1-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>