KVM: RISC-V: refactor vector state reset

Do not depend on the reset structures.

vector.datap is a kernel memory pointer that needs to be preserved as it
is not a part of the guest vector data.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Radim Krčmář <rkrcmar@ventanamicro.com>
Link: https://lore.kernel.org/r/20250403112522.1566629-4-rkrcmar@ventanamicro.com


Signed-off-by: Anup Patel <anup@brainfault.org>