RISC-V: KVM: Convert extension_disabled[] to ext_status[]

Change the boolean extension_disabled[] array to an array of enums,
ext_status[]. For now, the enum only has two states, which correspond
to the previous boolean states, so this patch has no intended
functional change. The next patch will add another state, expanding
the purpose of ext_status[].

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