RISC-V: KVM: Factor-out ONE_REG related code to its own source file

The VCPU ONE_REG interface has grown over time and it will continue
to grow with new ISA extensions and other features. Let us move all
ONE_REG related code to its own source file so that vcpu.c only
focuses only on high-level VCPU functions.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

arch/riscv/kvm/Makefile

@@ -19,6 +19,7 @@ kvm-y += vcpu_exit.o
 kvm-y += vcpu_fp.o
 kvm-y += vcpu_vector.o
 kvm-y += vcpu_insn.o
+kvm-y += vcpu_onereg.o
 kvm-y += vcpu_switch.o
 kvm-y += vcpu_sbi.o
 kvm-$(CONFIG_RISCV_SBI_V01) += vcpu_sbi_v01.o