KVM: arm64: nv: Handle SEAs due to VNCR redirection

System register accesses redirected to the VNCR page can also generate
external aborts just like any other form of memory access. Route to
kvm_handle_guest_sea() for potential APEI handling, falling back to a
vSError if the kernel didn't handle the abort.

Take the opportunity to throw out the useless kvm_ras.h which provided a
helper with a single callsite...

Cc: Jiaqi Yan <jiaqiyan@google.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250729182342.3281742-1-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>