KVM: selftests: fix supported_flags for riscv

commit 849c1816 ("KVM: selftests: fix supported_flags for aarch64")
fixed the set-memory-region test for aarch64 by declaring the read-only
flag is supported. riscv also supports the read-only flag. Fix it too.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20240403123300.63923-2-ajones@ventanamicro.com


Signed-off-by: Sean Christopherson <seanjc@google.com>