include: Sync-up encoding with priv v1.12-draft and hypervisor v0.5-draft

This patch sync-up encoding header with the latest privilege
specifications draft v1.12 and hypervisor specifications draft v0.5.

The MSTATUS.MTL and HSTATUS.STL bits are not present anymore and
will be removed by another patch series for hypervisor v0.5-draft.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>