KVM: selftests: Init IDT and exception handlers for all VMs/vCPUs on x86

Initialize the IDT and exception handlers for all non-barebones VMs and
vCPUs on x86.  Forcing tests to manually configure the IDT just to save
8KiB of memory is a terrible tradeoff, and also leads to weird tests
(multiple tests have deliberately relied on shutdown to indicate success),
and hard-to-debug failures, e.g. instead of a precise unexpected exception
failure, tests see only shutdown.

Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Link: https://lore.kernel.org/r/20240314232637.2538648-11-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>