KVM: arm64: Inject UNDEF for a register trap without accessor

KVM: arm64: Inject UNDEF for a register trap without accessor

Configuring a register trap without specifying an accessor function is
abviously a bug. Instead of calling die() when that happens, let's be a
bit more helpful and print the register encoding. Also inject an
undefined instruction exception in the guest, similar to other unhandled
register accesses.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Link: https://msgid.link/20251216103053.47224-3-alexandru.elisei@arm.com
Signed-off-by: Oliver Upton <oupton@kernel.org>