arm/gic: Detect broken configurations

Some virtualization platforms provide broken configurations. There
is a GIC interrupt controller, however accessing the CPU interface
registers leads to an external data abort. As these are needed to
handle interrupts we are unable to boot further.

Detect this misconfiguration and panic to tell the user the issue.

Reviewed by: emaste
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D54832

(cherry picked from commit 6c5fdba45a63d66984e15ddc6996f5e88a55f22c)