KVM: RISC-V: Do arch init directly in riscv_kvm_init()

Fold the guts of kvm_arch_init() into riscv_kvm_init() instead of
bouncing through kvm_init()=>kvm_arch_init().  Functionally, this is a
glorified nop as invoking kvm_arch_init() is the very first action
performed by kvm_init().

Moving setup to riscv_kvm_init(), which is tagged __init, will allow
tagging more functions and data with __init and __ro_after_init.  And
emptying kvm_arch_init() will allow dropping the hook entirely once all
architecture implementations are nops.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Anup Patel <anup@brainfault.org>
Message-Id: <20221130230934.1014142-25-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>