ANDROID: KVM: arm64: Set unknown bits of CONTEXTIDR_EL1 and VBAR_EL1

According to the architecture spec, the value of CONTEXTIDR_EL1
and VBAR_EL1 is mostly unknown. Set those unknown bits to an
easily recognizable value. These registers are often some of the
more problematic registers when it comes to debugging, and
therefore having that value would aid in debugging a guest.

Bug: 357781595
Change-Id: I440cd1b28e7b1a6df4511f7d39df710269b3f657
Signed-off-by: Fuad Tabba <tabba@google.com>