KVM: arm64: Add config register bit definitions

Add hardware configuration register bit definitions for HCR_EL2
and MDCR_EL2. Future patches toggle these hyp configuration
register bits to trap on certain accesses.

No functional change intended.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210817081134.2918285-11-tabba@google.com